Class 10 Science Chapter 11 Human Eye And Colourful World Short Answer Questions

Human Eye And Colourful World Short Answer Questions

Question 1. A star appears slightly higher than its actual position in the sky. Explain it.
Answer: It is due to atmospheric refraction. When the light of a star enters into the atmosphere, it is refracted continuously. The higher level of air acts as a rarer medium while the dense air near the surface of the earth acts as a denser medium. So, the atmosphere bends the starlight towards the normal.

As a result, the apparent position of stars is slightly different from its actual position. Thus the star appears slightly higher than its actual position in the sky.

Question 2. When we place a glass prism in the path of a narrow beam of white light, a spectrum is obtained. What happens when a second identical prism is placed in an inverted position to the first prism? Draw a labelled ray diagram to illustrate it.

The second prism recombines the spectrum obtained by the first prism. So from the other side of the second prism, n beam of white light is again obtained.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Second Prism

Question 3. With the help of scattering of light, explain the reason for the difference in colours ofthe sun as it appears during sunrise/sunset and noon.
Answer: The sun appears reddish at sunrise as well as at sunset and appears white at noon when it is overhead.

At sunrise/sunset, the blue light of shorter wavelength gets scattered away while passing through the thicker layer of air/large distance through air and red light of longer wavelength reaches our eye.

At noon, the sun is overhead and the light of the sun travels a relatively shorter distance to our eyes little blue and violet colours are scattered, and white light reaches our eyes.

Question 4. Why do some people use bifocal lenses?
Answer: Some people suffer from both myopia and hypermetropia. Such people require bi-focal lenses. The upper part ofthe bi-focal lens is a concave lens used for distant vision while its lower part is a convex lens used for reading purposes. These days, refractive defects are also corrected by using contact lenses or through surgical interventions.

Question 5. What is the “power of accommodation ofthe eye”? What happens to the image distance when the object being viewed is moved away from the eye?
Answer: The power of accommodation of the eye is the ability of the eye lens to adjust its focal length to see nearby and distant objects.

Image distance in the eye is fixed, being equal to the distance of the retina from the eye lens.

Question 6. Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?
Answer: When light passes through a prism offers different refractive indices to the different wavelengths of light. Thus, each colour suffers a different deviation. The red light deviates the least.

Question 7. Calculate the maximum power of accommodation of a person having normal vision.

A person needs to use glasses to read a newspaper. Identify the defect in her vision and the type oflens she would need to correct it.

Sometimes when we enter into a dark room from bright sunlight we are unable to see objects. Why?

Answer: D = 25 cm, Now, P = 1/f- D = 100/D = 100/25 = 4 D, thus for a person having normal vision, the power of accommodation is about 4 dioptre.

Long-sightedness, a convex lens.

The pupil regulates and controls the amount of light entering the eye. In bright sunlight, the size ofthe pupil is small and when we enter a dark room it takes some time for the pupil to expand in size due to dim light.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World

Question 8. A person can see up to 3 metres only. Prescribe a lens for him so that he can see up to 12 metres.
Answer: Clearly, the lens used in this case should be such that the rays proceeding from a point distant 12 m from the eye should, after refraction, appear to come from a point distant 3 m from the eye. Here, u =- 12 m, v =- 3 m, /= ?

Using lens formula, \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)

⇒ \(\begin{aligned}
& =-\frac{1}{3}+\frac{1}{12} \\
& =-\frac{1}{4} \quad \text { or } f=-4 \mathrm{~m}
\end{aligned}\)

Thus, a concave lens of a focal length of 4 m should be used.

Question 9. A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World A narrow Beaam

  1. Trace it on your answer sheet and show the path of the emergent beam as observed on the screen DE.
  2. Write the name and cause ofthe phenomenon observed.
  3. Where else in nature is this phenomenon observed?
  4. Based on this observation, state the conclusion which can be drawn about the constituents of white light.

Answer: The diagram is shown below

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World The phenomenonis called dispersion of light

The phenomenon is called the dispersion of light. It is because ofthe reason that different wavelengths oflight travel at different speeds in the glass prism. In a rainbow. White light consists of seven different wavelengths viz. violet, indigo, blue, green, yellow, orange and red.

Question 10. A person with a myopic eye cannot see objects beyond a distance of 1.5 m. What would be the power ofthe corrective lens used to restore proper vision?
Answer: The remedial lens should make the object at infinity appear at the far point.

  1. For an object at infinity, u =-∞
  2. Far point distance of the defective eye, v =- 150 cm
  3. By lens formula,

⇒ \(\begin{aligned}
\frac{1}{f} & =\frac{1}{v}-\frac{1}{u} \\
& =\frac{1}{-150}-\frac{1}{-\infty} \\
& =-\frac{1}{150}+0
\end{aligned}\)

⇒ \(=-\frac{1}{150}\)

or, f=-150cm.

Power, \(\mathrm{P}=\frac{1}{f(\text { in } \mathrm{m})}\)

A negative sign shows that the remedial lens is concave.

Question 11. Why do we have two eyes for vision and not just one?
Answer: Advantage of binocular vision: There are many advantages of having two eyes instead of one. These are as follows.

  1. It gives a wider horizontal field of view of about 180°.
  2. It helps to detect even fainter objects.
  3. It provides a three-dimensional effect of objects around us.
  4. The two eyes give relief to each other after every fraction of a second.

Question 12. A person is unable to read a book clearly when kept at a distance of 25 cm from his eye. Name the defect. How can it be corrected? Draw ray diagrams for defective eye-corrected eyes and explain them.
Answer: Hypermetropia or long-sightedness.

It is corrected by using a convex lens of suitable focal length. The diagrams are as shown below:

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Hypermetropia or long sightedness.

Defective eye: Rays from the object at N are focused beyond the retina i.e., near point goes away from the eye.

Corrected eye: Using a converging lens makes the image at the retina.

Question 13. Explain why the colour of the clear sky is blue.
Answer: The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light.

These are more effective in scattering light of shorter wavelength at the blue end than light of longer wavelength at the red end. The red light has a wavelength about 1.8 times greater than that of blue light.

Thus, when sunlight passes through the atmosphere, the fine particles in the air scatter the blue colour (shorter wavelength) more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering.

Question 14. State the cause of dispersion, when white light enters a glass prism. Explain with a diagram.
Answer: Light is made up of different colours. Each colour travels at its speed inside a prism. Due to this, different light colours bend through different angles for the incident ray, as they pass through a prism. The red light bends the least while the violet the most.

Thus, the rays of each colour emerge along different paths and thus become distinct. It is the band of distinct colours that we see in a spectrum. The diagram is as shown.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Light is made-up of different colours

A beam of white light falling on a glass prism gets split up into seven colours marked 7 as shown in the diagram:

The colours at positions marked 3 and 5 are similar to the colour ofthe sky and the colour of gold metal respectively. Is the above statement made by the Is student correct or incorrect Justify?

Which of the above-shown positions corresponds approximately to the colour of:

  1. A Brinjal
  2. Danger Signal
  3. Neel Which Is Applied To The Clothes
  4. Orange

Answer: As a result of dispersion produced by the prism, the white light is split up into seven colours. These colours as we know are represented by the letters of the word ‘VIBGYOR’.

Thus, blue is in the 3rd position and yellow is in the 5th position. These are the colours of the sky and the gold medal respectively. Thus, the statement is correct.

The positions of the colours ofthe given objects are represented by:

  1. brinjal ……….7
  2. Danger singal…….1
  3. Neel ……….6
  4. Organe……2

Question 15. A person wears glasses of power -2.5 D. Is the person far-sighted or near-sighted? What is the point of the person without glasses?
Answer: P =- 2.5 D.

Negative power shows that the lens is concave, so the person is near-sighted.

⇒ \(\begin{aligned}
f & =\frac{1}{\mathrm{P}} \\
& =\frac{1}{-2.5} \mathrm{~m}=-\frac{2}{5} \mathrm{~m} \\
& =-40 \mathrm{~cm} \\
u & =-\infty, v=?
\end{aligned}\)

From the lens formula,

⇒ \(\frac{1}{v}=\frac{1}{f}+\frac{1}{u}=\frac{1}{-40}+\frac{1}{-\infty}=\frac{1}{-40}-0=-\frac{1}{40}\)

v=-40 cm

Thus, the far point of the eye is 40 cm from the eye.

Question 16. List two causes leading to myopia of the eye. Draw ray diagrams to show the image formation in case of defective eye and correct eye.
Answer: The two main causes of myopia are:

  1. The eyeball is longer than normal.
  2. Decrease in the focal length of the eye lens

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Image Formed By the Defective Eye

Question 17. A person needs a lens of power -2.5 dioptres for correcting his vision. Name the defect of vision he is suffering from. Which lens will he be using for the correction1? Also, find the focal length oflens.
Answer: The person is using a concave lens of power -2.5 D. The person is, therefore, suffering from myopia. He is using a concave lens for the correction of the eye. Since P =1If, therefore, f= 1/P = 1/2.5 = 0.4 m = 40 cm.

Question 18. Explain how a normal human eye can see distinctly the object placed at a distance as well as those placed at a nearer distance. What are the far point and near point of a normal human eye?
Answer: For seeing distant objects, the focal length ofthe eye lens should be large and for seeing near objects the focal length of the eye lens should be small.

The focal length of the eye lens can be adjusted with the help of ciliary muscles holding the lens in position. The far point and near point are at infinity and 25 cm respectively.

Question 19. Name the part of the eye where the image is formed by the eye lens. What is the nature ofthe image formed? How is this image sent to the brain?
Answer: The image of the object formed by the eye lens is at the retina of the eye. The image formed on the retina is real and inverted. The image is sent to the brain with the help of the optic nerve.

Question 20. An old person is unable to see nearby objects as well as distant objects, What defect of vision is he suffering from? What kind oflens will be required to see the nearby as well as distant objects? Give reasons.
Answer: Presbyopia.

He shall have to use both kinds of lenses, convex lens for long-sightedness and concave lens for short-sightedness.

Question 21. Why does the sun appear reddish early in the morning? Illustrate with the help of a labelled diagram.
Answer: It is due to the scattering of light. The light near the horizon passes thicker layers of air and a larger distance of the atmosphere; hence, most ofthe blue light is scattered away and longer wavelength reaches our eyes giving rise to the reddish colour of the sun.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Reddish colour of sun during sunrise and sunset

Question 22. Why does it take some time to see the objects in a dim room when we enter the room from the bright sunlight outside?
Answer: In bright light, the size ofthe pupil is small to control the amount of light entering the eye. When we enter a dim room, it takes some time so that the pupil to expand and allow more light to enter and help to see things.

Question 23. Why does it take some time to see objects in a cinema hall when we just enter the hall from, bright sunlight? Explain in brief
Answer: The pupil regulates and controls the amount oflight entering the eye. In bright sunlight, the size of the pupil is small and when we enter the cinema hall takes some time for the pupil to expand in size due to dim light.

Question 24. Describe the formation of the rainbow in the sky.
Answer: A rainbow is always formed in a direction opposite to that of the sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. Due to the dispersion oflight and internal deflection, different colours reach the observer’s eye.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Arainbow is always formedin a direction opposite to that ofthe sun

  1. What is meant by the least distance of distinct vision?
  2. How does the thickness ofthe eye lens change when we shift looking from a distant tree
    to reading a book?

Answer: It is the minimum distance, to which normal eyes can see two similar objects distinctly.

The eye lens is comparatively thicker while reading a book.

Question 25. To correct distant vision, a person needs a lens of power -5.5 dioptres, and to correct near vision, he needs a lens of power +1.5 dioptres. What is the focal length of the lens required for correcting distant vision and near vision?

Answer: Power of distance viewing part of the lens,

P1 =-5.5 D

The focal length of this part

⇒ \(f_1=\frac{1}{P_1}=\frac{1}{-5.5} \mathrm{~m}\)

= -18.73 cm.

As the power of the near-vision part is measured relative to the main part of the lens of power – 5.5 D, so we use

P1 + P2 = P

or — 5.5 + P2 = + 1.5

or P2 = + 6.5 D

Focal length near-vision part

⇒ \(\begin{aligned}
f_2 & =\frac{1}{\mathrm{P}_2}=\frac{1}{+6.5} \mathrm{~m} \\
& =+15.4 \mathrm{~cm}
\end{aligned}\)

Question 26. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power ofthe lens required to correct the problem1
Answer: The remedial lens should make the objects at infinity appear at the far point.

∴ For an object at infinity u =-∞

Far point distance of the defective eye, v =- 80 cm

By lens formula, \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-80}-\frac{1}{-\infty}=-\frac{1}{80}+0=-\frac{1}{80}\)

or f=-80cm

Power, \(\mathrm{P}=\frac{100}{f(\mathrm{in} \mathrm{cm})}\)

⇒ \(\begin{aligned}
& P=\frac{100}{-80} \\
& P=-1.25 D
\end{aligned}\)

A negative sign shows that the remedial lens is concave.

Question 27. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point ofthe normal eye is 25 cm.
Answer: The object placed at 25 cm from the correcting lens must produce a virtual image at 1 m or 100 cm.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Virtual Image

u = -25 cm, v =- 100 cm

By lens formula \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-100}-\frac{1}{-25}=-\frac{1}{100}+\frac{1}{25}=+\frac{3}{100}\)

or \(f=+\frac{100}{3} \mathrm{~cm}=+\frac{1}{3} \mathrm{~m}\)

Power, \(\mathrm{P}=\frac{1}{f}=+\frac{3}{1}=+3 \mathrm{D}\)

Question 28. Why is a normal eye not able to see the objects placed closer than 25 cm?
Answer: At a distance of less than 25 cm, the ciliary muscles cannot bulge the eye lens anymore, the object cannot be focussed on the retina and it appears blurred to the eye, as shown in the figure.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World At distance less than 25 cm

Object O within 25 cm from the eye is not focused on the retina and is seen blurred.

Question 29. What happens to the image distance in the eye when we increase the distance of an object from the eye?
Answer: Due to its property of accommodation, the eye lens of a normal eye forms images of objects at various distances on the same retina. So the image distance in the eye remains the same.

Question 30. Why do stars twinkle?
Answer: The apparent position of a star is slightly different from the actual position due to the refraction of starlight by the atmosphere. Due to the variation in the atmospheric conditions, the amount oflight from a particular star changes randomly with time. This gives rise to a twinkling effect of the star.

Question 31. Explain why the planets do not twinkle.
Answer: As the planets are much closer to the Earth, the amount oflight received from them is much greater and the fluctuations caused in the amount of light due to atmospheric refraction are negligible as compared to the amount oflight received from them.

Question 32. Why does the sun appear reddish early in the morning?
Answer: Early in the morning, the sun is near the horizon. Sunlight reaches us after covering a large thickness ofthe atmosphere.

So shorter waves of blue region are almost completely scattered away by the air molecules. Red waves of longer wavelength are least scattered and reach our eyes. The sun appears red.

Question 33. Why does the sky appear dark instead of blue to an astronaut?
Answer: The atmosphere is quite thin at very high altitudes. There is almost no scattering of sunlight. So the sky appears dark to an astronaut.

Question 34. What is meant by the power of accommodation of the eye?
Answer: The power of accommodation of the eye is the maximum variation of its power for focusing on near and far (distant) objects. for a normal eye, the power of accommodation is about four diopters.

Question 35. A student sitting at the back of the classroom cannot read the letters written on the blackboard. What advice will a doctor give to her? Draw a ray diagram for the correction ofthis defect.
Answer: The student is suffering from myopia or near-sightedness. In myopia, one can see nearby objects clearly but cannot see distant objects distinctly. The doctor advises a concave lens of suitable power to bring the image back into the retina.

The ray diagram for the correction of this defect is shown below

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Myopic Eye And Hypermetropic Eye

Question 36. A person needs a lens of power -4.5D for correction of her vision.

  1. What kind of defect in vision is she suffering from?
  2. What is the focal length ofthe corrective lens?
  3. What is the nature ofthe corrective lens?

Answer: As the power of the lens is negative, she must be suffering from myopia.

Power, P =- 4.50, focal length, f=?

⇒ \(\mathrm{P}=\frac{1}{f} \Rightarrow f=\frac{1}{\mathrm{P}}=\frac{1}{-4.5}=-0.222 \mathrm{~m}=-22.2 \mathrm{~cm}\)

The nature ofthe corrective lens is concave or divergent.

Question 37. How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out ofthe second prism as white light? Draw the diagram.
Answer: A narrow beam of white light incident on one prism emerges out of the identical prism placed in an inverted position to the first prism close to the first prism as shown in the figure given below.

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World A Narrow Beam Of White Light Incident On The Prism

Question 38. Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also, indicate the order of the colours ofthe spectrum obtained.
Answer:

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World The Spectrum

Question 39. Why do we see a rainbow in the sky only after rainfall?
Answer: We see a rainbow in the sky only after rainfall due to the dispersion of sunlight by tiny water droplets, present in the atmosphere due to rainfall. The water droplets act as a prism.

They refract and disperse the incident sunlight then reflect it internally and finally refract it again when it comes out of a raindrop hence due to the dispersion of light and internal reflection, rainbow formation takes place during rainfall.

Question 40. Why is the colour ofthe clear sky blue?
Answer: The blue colour of the clear sky is due to Rayleigh’s scattering of sunlight. The molecules of air and other fine particles in the atmosphere have sizes smaller than the wavelength of visible light.

These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end.

Question 41. What is the difference in colours of the sun observed during sunrise-sunset and noon? Explain each.
Answer: During sunrise/sunset, the sun looks reddish because, at this stage, rays from the sun have to travel a much larger part of the atmosphere. The red colour having the largest wavelength is scattered the least.

At noon, the sun is nearly overhead. The sunlight has to pass through a smaller portion of the earth’s atmosphere. the scattering is much less and hence the sun looks White.

Question 42. A child sitting in a classroom is not able to read the writing on the blackboard.

  1. Name the type of defect from which his eye is suffering.
  2. With the help of a ray diagram show how this defect can be remedied.

Answer: The child’s eye is suffering from the defect of myopia.

The defect can be removed by using a concave lens as shown in the figure below:

CBSE Class 10 Science Chapter 11 Human Eye And Colour Full World Correction Of Myopia

Question 43. Why do we have two eyes instead of one?
Answer: Two eyes are better than one eye because of the following reasons:

  • The field of view with two eyes is more than with one eye.
  • Two eyes give three three-dimensional pictures of an object whereas one eye gives only two dimensional picture of an object.

Human Eye And Colourful World Multiple Choice Questions

Question 1. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to

  1. Presbyopia.
  2. Accommodation.
  3. Near-Sightedness.
  4. Far-Sightedness.

Answer: 2. The ability of the eye to focus objects at different distances is called accommodation.

Question 2. The human eye forms the image of an object in its

  1. Cornea.
  2. Iris.
  3. Pupil.
  4. Retina.

Answer: 4. The human forms the image of an object at its retina.

Question 3. The least distance of distinct vision for a young adult with normal vision is about

  1. 25 m.
  2. 2.5 cm.
  3. 25 cm.
  4. 2.5 m.

Answer: 3. The least distance of distinct vision for a normal eye is 25 cm.

Question 4. The change in focal length of an eye lens is caused by the action of the

  1. Pupil.
  2. Retina.
  3. Ciliary Muscles.
  4. Iris.

Answer: 3. The change in the focal length of the eye is due to the action of ciliary muscles.

Question 5. A person cannot see distinct objects kept beyond 2m. This defect can be corrected by using a lens of power

  1. + 0.5D
  2. – 0.5 D
  3. + 0.2 D
  4. – 0.2 D

Answer: 2. – 0.5 D

Question 6. A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?

  1. The near point of his eyes has receded away
  2. The near point of his eyes has come closer to him
  3. The far point of his eyes has come closer to him
  4. The far point of his eyes has receded away

Answer: 1. The near point of his eyes has receded away

Question 7. A prism ABC (with BC as the base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in the figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky?

  1. 1
  2. 2
  3. 3
  4. 4

Answer: 2. 1

Question 8. At noon the sun appears white as

  1. Light Is Least Scattered
  2. All The Colours of white Light Are Scattered Away
  3. Blue Colour Is Scattered The Most
  4. Red Colour Is Scattered The Most

Answer: 1. Light Is Least Scattered

Question 9. Which of the following phenomena of light are involved in the formation of the rainbow?

  1. Reflection, Refraction And Dispersion
  2. Refraction, Dispersion And Total Internal Reflection
  3. Refraction, Dispersion And Internal Reflection
  4. Dispersion, scattering and total internal reflection

Answer: 3. Refraction, Dispersion And Internal Reflection

Question 10. The twinkling of stars is due to atmospheric

  1. Dispersion Of light By Water Droplets
  2. Refraction Of Light By Different Layers Ofvarying Refractive Indices
  3. Scattering Of light By Dust Particles
  4. Internal Reflection of Light By Clouds

Answer: 2. Refraction Of light By Different Layers Ofvarying Refractive Indices

Question 11. The clear sky appears blue because

  1. Blue Light Gets Absorbed In The Atmosphere
  2. Ultraviolet Radiations Are Absorbed In The Atmosphere
  3. Violet And Blue Lights Get Scattered More Than Lights Of All Other Colours By The
    Atmosphere
  4. Light all other Colours Is Scattered More Than The Violet And Blue Colourlights By The Atmosphere

Answer: 3. Violet And Blue Lights Get Scattered More Than Lights Of All Other Colours By The Atmosphere

Question 12. Which of the following statements is correct regarding the-propagation oflight of different colours of white light in the air?

  1. Red Light Moves the Fastest
  2. Blue Light Moves Faster Than Green Light
  3. All The Colours of white Light Move at the Same Speed
  4. Yellow Light Moves With The Mean Speed As That Ofthe Red And The Violet Light

Answer: 3. All The Colours of white Light Move With The Same Speed

Question 13. The danger signals installed at the top of tall buildings are red. These can be easily seen from a distance because among all other colours, the red light

  1. Is Scattered The Most By Smoke Or Fog
  2. Is Scattered The Least By Smoke Or Fog
  3. Is Absorbed The Most By Smoke Or Fog
  4. Moves Fastest In Air

Answer: 2. Is Scattered The Least By Smoke Or Fog

Question 14. Which of the following phenomena Contributes Significantly To The Reddish Appearance Of The Sun At Sunrise Or Sunset?

  1. Dispersion Of light
  2. Total Internal Reflection Of light
  3. Scattering Of light
  4. Reflection Of Light From The Earth

Answer: 2. Total Internal Reflection Oflight

Question 15. The Bluish Colour Of Water In Deep Sea Is Due To

  1. The Presence Of algae And other plants Found In Water
  2. Reflection Ofsky In Water
  3. Scattering Oflight
  4. Absorption Oflight By The Sea

Answer: 3. Scattering Of light

Question 16. When Light Rays Enter The Eye, Most of the refraction Occurs At The

  1. Crystalline Lens
  2. Outer Surface Of the Cornea
  3. Iris
  4. Pupil

Answer: 2. Outer Surface Of the Cornea

Question 17. The Focal Length Of The Eye Lens Increases When Eye Muscles

  1. Are Relaxed And Lens Becomes Thinner
  2. Contract And Lens Becomes Thicker
  3. Are Relaxed And Lens Becomes Thicker
  4. Contract And Lens Becomes Thinner

Answer: 1. Are Relaxed And Lens Becomes Thinner

Question 18. Which of the following Statements Is Correct?

  1. A Person With Myopia Can See Distant Objects Clearly
  2. A Person With Hypermetropia Can See Nearby Objects Clearly
  3. A Person With Myopia Can See Nearby Objects Clearly
  4. A Person With Hypermetropia Cannot See Distant Objects Clearly

Answer: 3. A Person With Myopia Can See Nearby Objects Clearly

Question 19. Tarun’s father is an eye surgeon. He persuaded his father to put a camp in his society to educate people about eye donation. Rohan made a banner. One donation can give eyevision to two blind persons.

  1. Name the part of the eye that is used, during eye transplant.
  2. Name the defect that can be corrected by this transplant.
  3. What value of Tarun is reflected?
  4. The defect is caused by to cornea.

Answer: 1. Cornea.

  1. A defect is caused by to cornea.
  2. Tarun shows sympathy, compassion and empathy in his behaviour.

CBSE Class 10 Science Chapter 12 Electricity Short Answer Questions

Chapter 12 Electricity Short Questions And Answers

Question 1. Redraw the circuit question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12Ω resistor. What would be the readings in the ammeter and the voltmeter?
Answer: The required circuit diagram is given below

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current The Circuit

Reading of ammeter, \(I=\frac{V}{R}\)
⇒ \(=\frac{6}{25}\)
= 0.24A

Reading of voltmeter V=I.R
0.24×12
= 2.88 v

Question 2. Judge the equivalent resistance when the following are connected:

  1. Inland 106£l,
  2. 1 £l and 103£l, and 106£l.

Answer: When the resistors are connected in parallel, the equivalent resistance is smaller than the smallest individual resistance.

Equivalent resistance < 1Ω.

Equivalent resistance <1Ω.

Read and Learn More CBSE Class 10 Science Short Answer Questions

CBSE Class 10 Science Chapter 12 Electricty

Question 3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Answer: The advantages of connecting electrical devices in parallel with the battery are as follows:

Each device gets the full battery voltage. The parallel circuit divides the current through the electrical devices. Each device gets proper current depending on its resistance. If one device is switched OFF/ON, others are not affected.

Question 4. Why does the 1 cord of an electric heater not glow while the heating element does?
Answer: Both the cord and the heating element ofan electric heater carry the same current. However, the heating element becomes hot due to its high resistance (H = I2Rf) and begins to glow. The cord remains cold due to its low resistance and does not glow.

Question 5. Compute the heat generated while transferring 96,000 coulombs of charge in one hour through a potential difference of 50 V.
Answer: Here, Q = 96,000 C, t = 1 hour = 3600 s, V = 50 V

The heat generated, H = VQ

H = 50 V x 96,000 C

H = 48,00,000 J.

Question 6. An electric iron of resistance 20H takes a current of 5 A. Calculate the heat developed in 30 seconds.
Answer: Here, R = 20 Q, 1 = 5 A, t = 3 s

Heat developed is

H= I2Rt

H=25x20x30

H=15000 J.

Question 7. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2h.
Answer:

Here, I = 5 A. V = 220 V, / = 2 h = 7200 s

Power, P = VI

=220×5

=1100W

Energy consumed = px

= 100wx7200s

=7,20,000J.

Question 8. Compare the power used in the 2Ω resistor in each of the following circuits: 1. a 6 V battery in series with 1Ω and 2 Ω resistors, and a 4 V battery in parallel with 12 Ω and 2Ω resistors.
Answer: The circuit diagram is shown in the figure

Total resistance R=1+2=3

Potential difference v=6v

Current \(\mathrm{I}=\frac{\mathrm{V}}{\mathrm{R}}=\frac{6 \mathrm{~V}}{3 \Omega}=2 \mathrm{~A}\)

Power used in 2Ω resistor = I2R= (2)2×2=8w.

The circuit diagram for this case is shown below:

Power used in 2Ω1 resistor \(\begin{aligned}
& =\frac{V^2}{R}=\frac{(4)^2}{2} \\
& =8 \mathrm{~W}
\end{aligned}\)

=8w

Question 9. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Answer: Total power consumed in the circuit = 100 + 60 = 160 W

voltage v=220

power =vI

Current \(I=\frac{\text { Power }}{V}\)

⇒ \(\begin{aligned}
& =\frac{160}{220} \\
& =0.727 \mathrm{~A} .
\end{aligned}\)

=0.727A

Question 10. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Answer: Energy used by 250 W TV set in 1 hour

= 250 W x 1 h = 250 Wh

Energy used by 1200 W toaster in 10 minutes.

= 1200 W x 12 min.

⇒ \(=1200 \mathrm{~W} \times \frac{12}{60} h\)

= 240 Wh

Thus, the TV set uses more energy than the toaster.

Question 11. An electric heater of resistance 8 Q draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.
Answer: Here, R = 8 £2,I = 15A, t = 2h

The rate at which heat is developed in the heater is equal to the power

Therefore \(\begin{aligned}
\mathrm{P} & =\mathrm{I}^2 \mathrm{R}=(15)^2 \times 8 \\
& =\mathbf{1 8 0 0} \mathbf{J s}^{-1}
\end{aligned}\)

Question 12. Explain why a conductor offers resistance to the flow of current. Differentiate between conductor, resistor, and resistance.
Answer: We know that the motion of electrons in an electric circuit constitutes an electric current. However, the electrons are not completely free to move within the conductor. They are restrained by the attraction of the atoms among which they move.

Conductor: Any substance that is capable of readily transmitting heat, electricity, etc., is called a conductor.

Resistor: A conductor having some appreciable resistance is called a resistor.

Resistance: It is the property of a material by which it opposes the flow of current through it.

2. A piece of wire of resistance 6Q is connected to a battery of12 V. Find the amount of current flowing through it. Now, the same wire is redrawn by stretching it to double its length. Find the resistance of the new (redrawn) wire.
Answer: Here, resistance (R) = 6 Q, potential difference (V) = 12 V

V=IR

Or \(I=\frac{V}{R}=\frac{12 \mathrm{~V}}{6 \Omega}=2 \mathrm{~A}\)

Original Resistance

⇒ \(\mathrm{R}=\rho \frac{l}{\mathrm{~A}}\)

If the wire is doubled, then its new lengthl’ = 21 and new area of cross-section \(\mathrm{A}^{\prime}=\frac{\mathrm{A}}{2} \text {. }\)

The New Resistance

⇒ \(\mathrm{R}^{\prime}=\rho \frac{l^{\prime}}{\mathrm{A}^{\prime}}=\rho \frac{2 l}{\frac{\mathrm{A}}{2}}=\frac{4 \rho l}{\mathrm{~A}}=4 \mathrm{R}\)

or R’ = 4R, i.e., the resistance increases to four times

Question 13. Mention the condition under which charges can move in a conductor. Name the device which is used to maintain this condition in an electric circuit.
Answer: Charges can move, if there is a potential difference across the two ends ofthe conductor. An electric cell or a battery consisting of one or more cells can maintain an electric current in an electric circuit.

Question 14. Define the term ‘volt’. State the relation between work, charge, and potential difference for an electric circuit. Calculate the potential difference between the two terminals of a battery, if100joules ofwork is required to transfer 20 coulombs of charge from one terminal ofthe battery to the other.
Answer: One-volt potential difference between two points in a current-carrying conductor when 1 joule of work is done to move a charge of coulomb from one point to the other.

The relation is V = W/Q

Given, W = 100 J, Q = 20, V = ?

Using the relation, V = W/Q, we have

V = 100/20 = 5 V

Question 15. (a) How is the direction of electric current related to the direction of flow of electrons in a wire? Calculate the current in a circuit, if 500 C of charge passes through it in 10 minutes.
Answer: The direction of electric current is opposite to the direction of flow of electrons in a wire.

Given Q = 500 C,

t = 10 minute

= 10 x 60 = 600 s,I = ?

Using the relation, \(I=\frac{Q}{T}\)

= 500/600=083A

Question 16. Define electric current and state its SI unit. With the help of Ohm’s law explain the meaning of 1-ohm resistance.
Answer: It is defined as the rate of flow of electric charge through an electric circuit. Its SI unit is ampere (A). Ohm’s law is V = IR Let V = 1 ohm and1=1 ampere, then R = 1 volt/1 ampere =1 ohm Thus, 1 ohm is the resistance of a conductor, under the effect of a potential difference of volt across it a current of ampere flows through it.

Question 17. Find the current drawn from the battery by the network of four resistors

CBSE Class 10 Science Chapter 12 Electrcity The battery by the network

Answer: Equivalent resistance of the given network is

⇒ \(\frac{1}{\mathrm{R}}=\frac{1}{\mathrm{R}_4}+\frac{1}{\mathrm{R}_1+\mathrm{R}_2+\mathrm{R}_3}=\frac{1}{10}+\frac{1}{10+10+10}\)

⇒ \(=\frac{1}{10}+\frac{1}{30}=\frac{3+1}{30}=\frac{4}{30}\)

⇒ \(\mathrm{R}=\frac{30}{4}=7.5 \Omega\)

⇒ \(\begin{aligned}
& \mathrm{I}=\frac{\mathrm{V}}{\mathrm{R}}=\frac{3}{7.5}=\frac{30}{75}=\frac{2}{5} \\
& \mathrm{I}=0.4 \mathrm{~A}
\end{aligned}\)

Question 18. State the formula co-relating the electric current flowing in a conductor and the voltage applied across it. Also, show this relationship by drawing a graph. What would be the resistance of a conductor, if the current flowing through it is 0.35 ampere when the potential difference across it is 1.4 volts?
Answer: It states that Physical conditions remain the same the current flowing through the conductor is directly proportional to the potential applied across its two ends.”

The graph is shown below

CBSE Class 10 Science Chapter 12 Electricy Resistance

Given V = 1.4 V,I = 0.35 A

Now, resistance is given by the expression

⇒ \(\mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}}=\frac{1.4}{0.35}=4 \Omega\)

Question 19. The resistivity of two elements A and B are 1.62 x 10~8 Q m and 520 x  respectively. Out ofthese two, name the element that can be used to make:

  1. The filament of the electric bulb.
  2. Wires for electrical transmission lines. Justify your answer in each case.

Answer: Element B: It has more resistivity (520 x 10-8 £2 m).

Element A: It has less resistivity and hence less heating effect/dissipation of energy during transmission of power.

Question 20. Draw the nature of the V-Igraph for a nichrome wire (V – Potential difference, I – Current) A metallic wire of625 mm in length offers a 4 12 resistance. If the resistivity ofthe metal is 4.8 x IQ-7 ohm-meter, then calculate the area of the cross-section of The wire. 
Answer: The graph is as shown:

CBSE Class 10 Science Chapter 12 Electricty A Metallic Wire

Given p = 4.8 x 10-7n m,

L = 625 mm = 0.625 m, R = 4 Q, A = ?

Using the expression \(\mathrm{R}=\frac{\rho \mathrm{L}}{\mathrm{A}}\) we have

⇒ \(A=\frac{\rho L}{R}\)

⇒ \(\begin{aligned}
& =\frac{4.8 \times 10^{-7} \times 0.625}{4} \\
& =0.75 \times 10^{-7} \mathrm{~m}^2
\end{aligned}\)

Question 21. Derive the relation R=R1+R2 + R3 when three resistors Rp R2 andR3 are connected in series in an electric circuit.
Answer: Consider three resistors of resistances, R1, R2, and R3 connected in series to a cell of potential V as shown in the figure. Since the three resistors are connected in series, therefore, the current through each of them is the same. By Ohm’s law

V1=iR1 V2=IR 2 V3=IR3

IfRs are the equivalent resistance ofthe series combination, then on applying a potential difference V across it, the same must flow through it.

Therefore,

V = IRS

v = v1 + v2 + v3

IRS = IR1 + IR2 + IR3

Rs = Rx + R2 + R3

Question 22. (a) Nichrome wire of length L and radius ‘R’ has a resistance of 10 Q. How would the resistance ofthe wire change when:

  1. only the length ofthe wire is doubled.
  2. only diameter ofthe wire is doubled1? Justify your answer.
  3. Why are elements of electrical heating devices made made-up of alloys?

Answer:

R⇒ L

So resistance becomes two times,

i.e., R = 2 x 10 = 20 Q.

⇒ \(\mathrm{R} \propto \frac{1}{\mathrm{~A}} \propto \frac{1}{\mathrm{D}^2}\)

So when the diameter is doubled, resistance becomes \(\frac{1}{4}[latex] of its original

i.ec., R=10/4=2.5

This is because alloys do not oxidize readily at high temperatures.

Question 23. Draw schematic diagrams ofan electric circuit comprising of3 cells and an electric bulb, ammeter, and plug-key in the ON mode and another with the same components but with two bulbs in parallel and a voltmeter across the combination.
Answer:

CBSE Class 10 Science Chapter 12 Electrcity a voltmeter across the combination.

Question 24. The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating ofthe filament in the two cases).
Answer: Given: = 24 W, Vx = 12 V, P2 = ?, V2 = 6 V

Using [latex]\begin{aligned}
\mathrm{P} & =\frac{\mathrm{V}^2}{\mathrm{R}} \\
\frac{\mathrm{P}_1}{\mathrm{P}_2} & =\frac{\mathrm{V}_1^2}{\mathrm{~V}_2^2}
\end{aligned}\)

⇒ \(\begin{aligned}
\mathrm{P}_2 & =\left(\frac{\mathrm{V}_2}{\mathrm{~V}_1}\right) \times \mathrm{P}_1 \\
& =\left(\frac{6}{12}\right)^2 \times 24 \\
& =\frac{1}{4} \times 24 \\
& =6 \mathrm{~W}
\end{aligned}\)

Question 25. How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb is 1200 Q? If in place of the bulb, a heater of resistance 100 Q is connected to the sources, calculate the current drawn by it.
Answer: Given: V:220 V, Rx = 1200 £2,1, =?

R2 = 100 Q, I2 =?

Using OHm’s Law

⇒ \(\begin{aligned}
\mathrm{V} & =\mathrm{I}_1 \mathrm{R}_1 \\
\mathrm{I}_1 & =\frac{\mathrm{V}}{\mathrm{R}_1} \\
& =\frac{220}{1200} \\
& =0.18 \mathrm{~A}
\end{aligned}\)

And, \(\begin{aligned}
\mathrm{I}_2 & =\frac{\mathrm{V}}{\mathrm{R}_2} \\
& =\frac{220}{100} \\
& =2.2 \mathrm{~A}
\end{aligned}\)

Question 26. Out of the two wires X and Y shown below, which one has greater resistance? Justify your answer.
Answer: Wire ‘Has greater resistance as it has more length than wire It is because the resistance of wire is directly proportional to the length of wire for the same area of cross-section for the same material.

Question 27. An electric iron has a rating of 750 W, 220 V. Calculate the current flowing through it, and its resistance when in use.
Answer: Given: P = 750 W, V = 220 V

p=VI

750=220xI

⇒\(I=\frac{750}{220}=3.40 \mathrm{~A}\)

⇒\(\begin{aligned}
\mathrm{P}=\frac{\mathrm{V}^2}{\mathrm{R}} \Rightarrow \mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}} & =\frac{220^2}{750} \\
& =64.53 \Omega
\end{aligned}\)

Question 28. Why is the parallel arrangement used in domestic wiring?
Answer: Parallel arrangement is used in domestic wiring because of the following:

All the appliances work at the same voltage as that of the electric supply.

If one ofthe appliances is out of order, e.g., if a bulb gets fused, all other appliances keep on working as the circuit is not broken in the parallel arrangement of devices.

Question 29. Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer: When the potential difference is halved, the current through the component also decreases to half of its initial value. This is per Ohm’s law, i.e., V °c I.

Question 30. On what factors does the resistance of a conductor depend?
Answer: The resistance of the conductor depends

  1. On its length,
  2. On its area of cross-section and the nature of its material.

Question 31. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer: The current will flow more easily through a thick wire than a thin wire of the same material. The larger the area of the cross-section of a conductor, the greater the ease with which the electrons can move through the conductor. Hence the lower the resistance of the conductor.

Question 32. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer: The coils of electric toasters and electric irons are made of alloys instead of pure metal due to the following reasons:

Alloys have higher resistivity than that of their constituent metals.

Alloys do not oxidize (or burn) readily at high temperatures.

Question 33. Use the data to answer the following:

  1. Which among iron and mercury is a better conductor?
  2. Which material is the best conductor?

Answer: Resistivity of iron = 10.0 x 10-8 ft m Resistivity of mercury = 94.0 x 10-8 ft m Thus, iron is a better conductor because it has lower resistivity than mercury.

As silver has the lowest resistivity (= 1.60 x 10-8 ft m), silvers are the best conductor.

Question 34. Draw a schematic diagram of a circuit consisting of a battery of three cells of Veach, a 5 ft resistor, an S ft resistor a 12 ft resistor, and a plug key, all connected in series.
Answer: The Required circuit diagram is shown

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current The Circuit

Question 35. What determines the rate at which energy is delivered by a current
Answer: The resistance of the circuit determines the rate at which energy is delivered by a current.

Question 36. How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer: A voltmeter is connected in parallel to measure the potential difference between two points in a circuit

Chapter 12 Electricity Multiple Choice Questions

Question 1. A piece of wire of resistance is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance ofthis combination is’, then the ratio’ is:

  1. 1/25
  2. 1/5
  3. 5
  4. 25

Answer: Resistance of each part= r/5

When the five parts are connected in parallel, the equivalent resistance R’ is given by

⇒ \(\begin{aligned}
& \frac{1}{\mathrm{R}^{\prime}}=\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}=\frac{25}{\mathrm{R}} \\
& \frac{\mathrm{R}}{\mathrm{R}^{\prime}}=25
\end{aligned}\)

Question 2. Which of the following terms does not represent electrical power in a circuit?

  1. IR2
  2. \P/R
  3. PR
  4. VI

Answer: IR2 does not represent electrical power.

Question 3. An electric bulb is rated 220 V and 100 W. When it is operated at 110 V, the power consumed will be:

  1. 75 W
  2. 25 W
  3. 100 W
  4. 50 W

Answer: 4. Resistance \(\mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}}\)

⇒ \(\begin{aligned}
& =\frac{(220)^2}{100} \\
& =484 \Omega
\end{aligned}\)

When operated at 110 V, the power consumed will be

⇒ \(\begin{aligned}
P^{\prime} & =\frac{V^2}{R} \\
& =\frac{(110)^2}{484} \\
& =25 \mathrm{~W}
\end{aligned}\)

Question 4. Two conducting wires ofthe same material and of equal lengths and equal diameters are first connected in series and then in parallel in a circuit across the same potential difference. The ratio of produced in series and parallel combinations would be

  1. 1:2
  2. 2:1
  3. 1:4
  4. 4:1

Answer: Let R be the resistance of each wire. In series combination, the total resistance will be 2R. Heat produced.

Question 2. Why do V birds sitting on live wire get an electric shock?
Answer: Birds when sitting on the live wire just add to the circuit, it does not get shocked because the current is not flowing out of their body to any other material.

Question 3. There is a frill of 20 bulbs connected in series in a room. One bulb gets fused. The remaining 19 are again joined in series and connected to the same supply. Will the light increase or decrease in the room?
Answer: The light will increase.If the voltage remains the same, then the power available to the frill
\(\mathrm{P}=\frac{\mathrm{V}^2}{\mathrm{R}}\) where R is resistance ofthe frill. When one bulb is removed, the resistance of the frill decreases and hence the power output will increase.

Question 4. Two perform the experiments on series and andparallel combinations of two given resistors R1 and R2 and plot the following V-Igraphs

CBSE Class 10 Science Chapter 12 Electricty R is Resistance of the Frill

Which of the graphs is (are) correctly labeled in terms ofthe words ‘series and ‘parallel’1? Justify your answer.
Answer: In a series combination for a given voltage, the current is less as compared to that in a parallel combination. Therefore, both graphs are labeled correctly.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current Short Answer Questions

CBSE Chapter 13 Magnetic Effects Of Electric Current Short Question And Answers

Question 1. List the properties of magnetic lines of force.
Answer: Those are closed curves that start in the air from the N-pole end at the S-pole and then return to the N-pole through the interior of the magnet.

  1. No two magnetic lines of force can intersect each other.
  2. The field lines are closer together in the regions of strong fields.
  3. The field lines tend to contract lengthwise and expand sidewise.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current

Question 2. Why don’t two magnetic lines of force intersect each other?
Answer: If two lines of force intersect, then there will be two directions of the magnetic field at the point of intersection and a magnetic needle placed at this point should point towards these two directions, which is not possible.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 3. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer: Each section of wire produces its concentric set of lines of force. By applying the right-hand thumb rule, we find that all the sections produce a magnetic field directed downward at all points inside the loop while at the outside points, the field is directed upwards. Hence, the magnetic field acts normally into the plane of paper at the points inside the loop and normally out ofthe plane of paper at points outside the loop.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric circular Loop Of Wire

Question 4. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field B can be represented by equidistant parallel lines of force, as shown in the figure.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Field Lines Of A Uniform Magnetic Field

Choose the correct option.

  1. The magnetic field inside a long straight solenoid-carrying current Is zero.
  2. Decreases as we move towards its end
  3. Increases as we move towards its end.
  4. Is the same at all points.

Answer: 4. It is the same at all points

Question 5. In Activity 7.7, how do we think the displacement of rod AB will be affected if current in rod AB is increased; a stronger horse-shoe magnet is used; and the length of the rod AB is increased?
Answer: When the current in the red AB is increased, the force exerted on the conductor increases, so the displacement of the rod increases.

When a stronger horse-shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod. (Hi) Displacement of the rod is directly proportional to its length. Hence, there would be a larger displacement if the length of the rod AB is increased.

Question 6. State Fleming’s left-hand rule.
Answer: According to Fleming’s left-hand rule, if we stretch the forefinger, the middle finger and the thumb of our left hand are mutually perpendicular to each other and if the forefinger points in the direction ofthe magnetic field, the middle finger in the direction of current, then the thumb will point in the direction of motion or the force on the conductor.

Question 7. What is the principle ofan electric motor?
Answer: A current-carrying conductor when placed in a magnetic field experiences a force. The direction ofthis force is given by Fleming’s left-hand rule. This is the basis of an electric motor.

Question 8. What is the role ofthe split ring in an electric motor?
Answer: The split ring reverses the direction of current in the armature coil after every half rotation, i.e., it acts as a commutator. The reversed current reverses the direction ofthe forces acting on the two arms of the armature after every half rotation. This allows the armature coil to rotate continuously in the same direction.

Question 9. Explain different ways to induce a current in a coil.
Answer: A current can be induced in a coil by

  1. If moving a magnet towards or away from the coil or vice versa, and
  2. Changing current in the neighboring coil

Question 10. State the principle ofan electric generator.
Answer: An electric generator works on the principle of electromagnetic induction. When a closed coil is rotated in a uniform magnetic field with its axis perpendicular to the direction of the field, the magnetic field lines passing through the coil change and induce potential difference and hence a current is set up.

Question 11. Name some sources of direct current.
Answer: Some of the sources of direct current are dry cells, button cells, lead accumulators, etc.

Question 12. Which sources produce alternating current?
Answer: Alternating current is produced by A.C. generators of nuclear power plants, thermal power plants, hydroelectric power stations, etc.

Question 13. An electric oven with a kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer: The electric oven draws a current given by

⇒ \(\begin{aligned}
& \mathrm{I}=\frac{\mathrm{P}}{\mathrm{V}}=\frac{2 \mathrm{~kW}}{220 \mathrm{~V}} \\
& \mathrm{I}=\frac{2000 \mathrm{~W}}{220 \mathrm{~V}} \\
& \mathrm{I}=9.09 \mathrm{~A}
\end{aligned}\)

Thus, the electric oven draws current much more than the current rating of A. That is the circuit is overloaded. Due to excessive current, the fuse wire blows, and the circuit is broken.

Question 14. What precautions should be taken to avoid the overloading of domestic electric circuits?
Answer: As a result of overloading, the connecting wires get overheated and the appliances may get damaged.

To avoid this, the following safety measures must be taken:

The wires used in the circuit must be coated with good insulating materials like PVC, etc.

The circuit must be divided into different sections and a safety fuse must be used in each section. High-power appliances like air-conditioners, refrigerators, water heaters, etc., should not be used simultaneously.

Question 15. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet1? Explain.
Answer: The magnetic field pattern produced by a solenoid is similar to that of a bar magnet.
Like a bar magnet, one end of the solenoid has N-polarity and the other end has Spolarity.

We bring the N-pole of the bar magnet near one end of the solenoid. If there is an attraction, then that end of the solenoid has south polarity and the other has north polarity. If there is a repulsion, then that end ofthe solenoid has north polarity and the other end has south polarity.

Question 16. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer: When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

Question 17. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer: According to Fleming’s left-hand rule, the magnetic field acts in a vertically downward direction. Note that the direction of the current will be opposite to that ofthe electron beam.

Question 18. Name some devices in which electric motors are used.
Answer: Electric motor is used ’n appliances like electric fans, washing machines, mixers, grinders, blenders, computers, MP3 players, etc.

Question 19. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is pushed into the coil, withdrawn from inside the coil, or held stationary inside the coil?
Answer: An electric current is induced in the coil and the galvanometer shows a deflection.

An electric current is induced in the coil but in the opposite direction. The galvanometer shows a deflection in the reverse direction.

No current is induced in the coil. The galvanometer shows no deflection.

Question 20. Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in the coil B? Give a reason.
Answer: Yes. When the current in coil A is changed, some current is induced in the coil B. Due to the change in current in coil A, the magnetic field lines linked with coil A and coil B get changed. This sets up induced current in coil B.

Question 21. State the rule to determine the direction of a magnetic field produced around a straight conductor-carrying current, the force experienced by a current-carrying straight conductor placed in a magnetic field that is perpendicular to it, and the current induced in a coil due to its rotation in a magnetic field.
Answer: Right-hand thumb rule: If the current-carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

Fleming’s left-hand rule: Stretch the forefinger, the middle finger and the thumb ofthe left hand mutually perpendicular to each other. The forefinger points in the direction ofthe magnetic field, the middle finger in the direction of the current, then the
thumb points in the direction of force in the conductor.

Fleming’s right-hand rule: Stretch the thumb, forefinger, and middle finger of the right hand mutually perpendicular to each other.If the forefinger points in the direction of the magnetic field, the thumb in the direction of motion of the conductor, then the middle finger points in the direction of the current induced in the conductor.

Question 22. When does an electric short circuit occur?
Answer: As a result of the live wire touching the neutral wire, the resistance offered to the flow of current becomes almost zero and this is called short-circuiting. In this situation, a large current flows through the circuit, causing a spark or damage to the appliance.

Question 23. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The earth wire connects the metallic body ofthe high-powered appliance to the earth. It is a safety measure that ensures any leakage of current of the metallic body of the appliance as it keeps its potential equal to that ofthe earth (zero volts) and the user may not get a severe electric shock.

Question 24. The horizontal component of Earth’s magnetic field at a place is uniform and its direction is south to north. A high current through a horizontal power line flows at this place from west to east. Consider two points A and B at equal distances from the wire, respectively above and below it. Giving reason explains where the fields are A and B.
Answer: According to the right-hand thumb rule, the direction of the magnetic field due to the current at A is from north to south and at B from south to north.

Therefore, at A earth’s field and field due to current are in opposite directions whereas at B they are in the same direction. So the field is more at B.

Question 25. Give some advantages of electromagnets over permanent magnets.
Answer: An electromagnet has the following advantages over a permanent magnet:

  1. An electromagnet can produce a very strong magnetic field.
  2. The strength of the magnetic field of an electromagnet can be increased/decreased by increasing/decreasing the strength of the current or the number of turns in the solenoid.
  3. The polarity of an electromagnet can be reversed by sending the current in the reverse direction.

Question 26. Name and state the rule to determine the direction of force experienced by a straight conductor carrying current placed in a magnetic field that is perpendicular to it. Or State Fleming’s left-hand rule with a labeled diagram.
Answer: Fleming’s left-hand rule: Stretch the forefinger, the central finger, and the thumb of the left hand mutually perpendicular to each other. The forefinger points in the direction of the magnetic field, the central finger in the direction of current, and then the thumb points in the direction of force on the conductor.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current Fleming Left Hand Rule

Question 27. Two long parallel wires are hanging freely. If they are connected to a battery (i) in series and 2 in parallel, what would be the effect on their positions?
Answer: In series: The current flowing in them will be in the opposite direction. Hence, they will repel each other.

In parallel: The current flowing in them will be in the same direction. Hence, they will attract each other.

Question 28. What is the role of the fuse, used in series with any electrical appliance? Why should a fuse with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it.

If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off.

Question 29. A current through a horizontal power line flows in an east-to-west direction. What is the direction magnetic field at a point directly below it and a point directly above it?
Answer: The current is in the east-west direction. Applying the right-hand thumb rule, we get that the direction of the magnetic field at a point below the wire is from north to south. The direction of the magnetic field at a point directly above the wire is from south to north.

Question 30. Explain why a fuse should be joined with the live wire and not with the neutral wire in a domestic circuit.
Answer: In a domestic circuit, the phase wire always has a much higher potential than the neutral wire. Moreover, the neutral wire is connected to the earth at the substation. Thus, during a short circuit, the fuse will break the connection with the neutral wire and not the live wire.

Question 31. A current I passes through a circular loop C and a solenoid AB as shown below:

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric LoopC

  1. What is the polarity of (a) the force ofthe loop you are looking at? (b) the end of the solenoid?
  2. What is the direction ofthe magnetic field at the center ofthe loop?

Answer: The face of the loop will behave as a North Pole.

  1. End B will also behave as a North Pole.
  2. Straight and parallel to the axis of the solenoid.

Question 32. Can two magnetic lines of force intersect? Justify your answer.
Answer: No, if two magnetic lines of forces intersect, then there will be two tangents and hence two directions of the magnetic field at the point of intersection. This is not possible.

Question 33. Define a solenoid. How is it different from a coil? 
Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The strength of the magnetic field inside a coil varies while in the solenoid case, it is the same.

Question 34. State Faraday’s Laws of electromagnetic induction.
Answer: Faraday put forward the following laws: Faraday’s laws of electromagnetic induction.

  1. Whenever the magnetic field (flux) linked with a coil changes, an induced EMF is produced.
  2. The induced emflasts as long as the change in magnetic field (flux) continues.
  3. The induced emf in the closed loop equals the negative rate of change of magnetic field (flux) through the loop.

Question 35. State Oersted observation. How can it be shown that a magnetic field exists around a wire through which a direct electric current is passing?
Answer: A magnetic needle brought close to a straight current-carrying wire aligns itself perpendicular to the wire, reversing the direction of current reverses the direction of deflation. This shows that the current-carrying wire is associated with a magnetic field.

Question 36. Draw the patterns of magnetic field lines due to a bar magnet. The magnetic field lines
are closed curves. Why?
Answer: Inside the magnet, the direction of field lines is from its south pole to its north pole. So the magnetic field lines are closed curves

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Inside the magnet

Question 37. An alpha particle (+ve charged particle) enters a magnetic field at a right angle as shown in the figure. Explain with the help of a relevant rule, the direction of force acting on the alpha particle.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Magnetic Field

Answer: According to Fleming’s left-hand rule, if the forefinger points in the direction ofthe magnetic field and the central finger points in the direction of a current, the thumb gives the direction of the force acting on the conductor. So the force will act in the upward direction of the alpha particle.

Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors that can produce them.

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric The Type Of Manetic Field By Represented by the magnetic field

Answer: It represents the magnetic field lines produced by a current-carrying circular loop.

It represents the magnetic field lines produced by a solenoid

Question 38. Explain the right-hand thumb rule and cork and screw rule to find the magnetic field due to a current-carrying conductor.
Answer: Imagine a current-carrying conductor held in your right hand such that the thumb points in the direction of current, then the curl of your fingers encircling the conductor will give the direction of magnetic field lines around the conductor. Maxwell’s cork screw rule (Right-hand screw rule):

Imagine a right-handed screw to be rotated in the direction of current, then the direction of rotation gives the direction of magnetic field lines.

Question 39. What is the nature of the magnetic field produced by a current-carrying circular coil? Explain with the help ofan experiment.
Answer: Bend a copper wire in a circular shape. Pass the coil through a cardboard. Connect the free ends ofthe coil to a battery and a key. Sprinkle some iron filings on the cardboard.

Put on the key, you will find that the iron filings arrange themselves in the form of concentric circles. The magnetic lines of force near each segment of wire are circular and form concentric circles. Whereas the lines of force near the center of the coil are almost straight fines. Note that at the center of the coil, the magnetic field is uniform and perpendicular to the plane of the coil.

Question 40. In a pattern of magnetic field lines due to a bar magnet, how can the regions of relative strength be identified1? Compare the strength of the field near the poles and middle of a bar magnet
Answer:

The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field fines.

The strength of the field near the poles is highest and in the middle of a bar magnetite is the lowest.

Question 41. State one main difference between AC and DC. Why ac is preferred over DC for long-range transmission of electric power? Name one source for each of DC and AC.
Answer: The DC always flows in one direction while AC reverses its direction periodically. This is because in the case of AC electric power can be transmitted over long distances without much loss of energy.

  1. Source of AC- AC generator
  2. Source of- DC generator/cell

Question 42. Student experiments to study the magnetic effect of current around a current-carrying straight conductor with the help of a magnetic compass. He reports that:

  1. The degree of deflection ofthe magnetic compass increases when the compass is moved away from the conductor.
  2. the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
  3. Which of the above observations ofthe student appears to be wrong and why?

Answer: The first observation is wrong. Because as the distance from the conductor increases, the strength ofthe magnetic field will decrease. So the degree of deflection ofthe compass should decrease instead of increasing.

Question 43. Draw magnetic field lines produced around a current carrying a straight conductor passing through cardboard. How will the strength of the magnetic field change, when the point where the magnetic field is to be determined, is moved away from the straight wire carrying constant current? Justify your answer:
Answer: The diagram is as shown:

We will move a compass needle away from the straight wire. When it is moved away from the straight wire, the deflection of the needle decreases which implies that the strength of the magnetic field decreases.

Question 44. A student while studying the force experienced by a current-carrying conductor in a magnetic field records the following observations.

  1. The force experienced by the conductor increases as the current is increased.
  2. The force experienced by the conductor decreases as the strength ofthe magnetic field is increased
  3. Which of the two observations is correct and why?

Answer: The observation is correct.

Question 45. Magnetic field lines are shown in the given diagram. A student makes a statement that the magnetic field at X is stronger than at Y. Justify this statement. Also, redraw the diagram and mark the direction of magnetic field lines.
Answer: The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field lines. The field lines are closer at X than at Y. Therefore, the field is stronger at X where the field lines are crowded. The diagram is as shown:

Because the force experienced by a current-carrying conductor in a magnetic field is proportional to the strength of the current.

Question 46. How does the strength ofthe magnetic field at the center of a circular coil of a wire depend on:

  1. Radius Ofthe Coil
  2. Number of Ofturns In The Coil

Answer: 1 As the radius increases, the field decreases.

2. The field produced is directly proportional to the number of turns in the coil.

Question 47. What is a fuse? How does it function?
Answer: An electric fuse is a device that is used to limit the current in an electric circuit. The use of a fuse is to safeguard the circuit and the appliances connected to it from being damaged.

The fuse is a short piece of wire made of a material having a low melting point. When an electric current is passed through it, the fuse gets heated. If the current passing through the fuse exceeds the safe limit, the heat produced melts the fuse and this breaks the circuit.

Question 48. What is meant by the term “magnetic field lines”? List two properties of magnetic field lines.
Answer: A magnetic field line is a path that will be followed by a “hypothetical” north pole in the magnetic field of another magnetite that is allowed to move freely. Two properties of magnetic field lines are:

  1. Two magnetic field lines do not intersect each other.
  2. They travel from the north to the south pole of a magnet outside the magnet and from the south to the north pole inside the magnet.

Question 49. Draw a rough sketch of the pattern of the field lines due to:

  1. Current flowing into a circular coil and
  2. Solenoid carrying current

Answer: The sketches are shown below:

CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Solenoid Carrying Current

Question 50. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected, if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength of the magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 51. As shown in the figure, a magnetic compass needle is placed on a paper plane near point A. In which plane should a straight current-carrying conductor be positioned so that it passes through A and there is no change in the deflection ofthe compass? Under what condition is the deflection maximum and why?
Answer: In the plane of the paper itself. The axis of the compass is vertical and the field due to the conductor is also vertical. It could result in a dip of the compass needle which is not possible in this case (dips result only if of compass is horizontal). The deflection is maximum when the conductor through Ais perpendicular to the plane paper and the field due to its maximum in the plane of the paper.

Question 52. Under what conditions permanent electromagnet is obtained if a current-carrying solenoid is used? Support your answer with the help of a labeled circuit diagram.
Answer: The current through the solenoid should be a direct current.

The rod inside is made of a magnetic material such as steel.

Question 53. AB is a current-carrying conductor in the plane of the paper as shown in the figure. What are the directions of the magnetic field produced by it at the points P and Q? Given; > r2, where will the strength ofthe magnetic field be larger?
Answer: Into the plane of paper at P and out of at Q. The strength of the magnetic field is larger at the point located closer i.e. at Q

Question 54. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 55. It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving alpha particles, and neutrons’? Justify your answer.
Answer:

  1. Yes, Alpha particles being positively charged constitute, current to the direction of motion.
  2. No, the neutrons being electrically neutral constitute no current.

Question 56. What does the direction of thumb indicate in the right-hand thumb rule? In what way
this rule is different from Fleming’s left-hand rule?
Answer: The thumb indicates the direction of current in the straight conductor held by curled fingers, whereas Fleming’s left-hand rule gives the direction of force experienced by the current-carrying conductor placed in an external magnetic field.

Question 57. Meena draws magnetic field lines of field close to the axis of a current-carrying circular
loop. As she moves away from the center ofthe circular loop she observes that the lines keep
on diverging. How will you explain her observation?
Answer: The strength of the magnetic field falls as distance increases. This is indicated by the decrease in the degree of closeness of the lines of field.

Question 58. What does the divergence of magnetic field lines near the ends of a current carrying a straight solenoid indicate?
Answer: The divergence, that is, the falling degree of closeness of magnetic field lines indicates
the fall in strength of the magnetic field near and beyond the ends of the solenoid.

Question 59. Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?
Answer: Electric fans, mixers, washing machines, computer drives, etc. Motors convert electrical energy into mechanical energy whereas generators convert mechanical energy into electrical energy.

Question 60. What is the role ofthe two conducting stationary brushes in a simple electric motor?
Answer: The brushes are connected to the battery and touch the outer side of two halves of the split ring whose inner sides are insulated and attached to the axle.

Question 61. What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?
Answer: Direct current always flows in one direction but the alternating current reverses its direction periodically. The frequency of AC in India is 50 Hz and in each cycle it alters direction twice. Therefore AC changes direction 2 x 50 = 100 times in one second.

Question 62. What is the role of the fuse, used in series with an electrical appliance? Why should a fuse
with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it. If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off. This practice of using a fuse of improper rating should always be avoided.

Question 63. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current-carrying loop is brought near it? Describe some salient features of the magnetic lines of field concept.
Answer: Current carrying loops behave like bar magnets and both have their associated lines of field. This modifies the already existing earth’s magnetic field and a deflection results. The magnetic field has both direction and magnitude. Magnetic field lines emerge from the N-pole and enter the S-pole.

The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.

Question 64. With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying a straight long conducting wire. How is the right-hand thumb rule useful to find the direction of the magnetic field associated with a current-carrying conductor?
Answer: The right-hand thumb rule states that if a current-carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction ofthe field lines of the magnetic field.

Question 65. Explain with the help of a labeled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn?
Answer:
The magnetic field (B) produced by current carrying N circular wire depends on:

  • Amount of current flowing through wire (I):
    • B∞I
  • Number of turns on the circular wire (N)
    • B∞N

If there is a circular coil having N turns, the field Magnetic force (lines) due to produced is N times as large as that produced by a current carrying through a loop single turn.

Magnetic Effects Of Electric Current Multiple-Choice Questions

Question 1. Choose the incorrect statement from the following regarding magnetic lines of the field.

  1. The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
  2. Magnetic field lines are closed curves
  3. Magnetic field lines are parallel and equidistant, they represent zero field strength
  4. The relative strength of the magnetic field is shown by the degree of closeness of the field lines.

Answer: 3. If magnetic field lines are parallel and equidistant, they represent zero field strength

Question 2. If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

  1. Concentric Circles
  2. Elliptical In Shape
  3. Straight Lines Parallel to Each Other
  4. Concentric Circles Near The Point O But Of Elliptical Shapes As We Go Away From It

Answer: 3. Straight Lines Parallel to Each Other

Question 3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anticlockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to

  1. A
  2. B
  3. A if the current is small, and B if the current is large
  4. B if the current is small and the current is large

Answer: 1. A

Question 4. For a current in a long straight solenoid, N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is

  1. The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all the points inside the solenoid
  2. The strong magnetic field produced inside the solenoid can be used to magnetize a piece of magnetic material like soft iron when placed inside the coil
  3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet
  4. The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Answer: 3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet.

Question 5. A uniform magnetic field exists in the plane of paper pointing from left to right as shown in the given figure. In the field an electron and a proton move as shown. The electron and the proton experience

  1. Forces Both Pointing Into The Plane of Paper
  2. Forces Both Pointing Out Ofthe Plane Of paper
  3. Forces Pointing Into The Plane Ofpaper And Out Of The Plane Ofpaper, Respectively
  4. Force Pointing Opposite And Along The Direction Of The Uniform Magnetic Field Respectively

Answer: 1. Forces Both Pointing Into The Plane Ofpaper

Question 6. Commercial electric motors do not use

  1. An Electromagnet To Rotate The Armature
  2. Effectively Large Number of Turns of Ofconducting Wire In The Current Carrying Coil
  3. A Permanent Magnet To Rotate The Armature
  4. A Soft Iron Core On Which The Coil Is Wound

Answer: 3. A Permanent Magnet To Rotate The Armature

Question 7. In the arrangement shown in given figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then

  1. The Deflection In Thegalvanometerremains Zero Throughout
  2. There Is A Momentary Deflection In The Galvanometer But It Dies Out Shortly And There Is No Effect When The Key Is Removed
  3. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In The Same Direction
  4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Answer: 4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Question 8. Choose the incorrect statement

  1. Fleming’s right-hand rule is a simple rule to know the direction of the induced current
  2. The right-hand thumb rule is used to find the direction of magnetic fields due to current-carrying conductors
  3. The difference between the direct and the alternating current is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
  4. In India, the AC changes direction after every — second.

Answer: 4. In India, the AC changes direction after every — second.

Question 9. A constant current flows in a horizontal wire in the plane ofthepaper from the east to the west as shown in the figure. The direction of the magnetic field at a point will be North to South

  1. Directly Above The Wire
  2. Directly Below The Wire
  3. At A Point Located In The Plane Of The Paper, On The North Side Of The Wire
  4. At A Point Located In The Plane Ofthe Paper, On The South Side Ofthe Wire

Answer: 2. Directly Below The Wire

Question 10. The Strength Magnetic Field Inside A Long Current Carrying a Straight Solenoid Is

  1. More At The Ends Than At The Centre
  2. Minimum In The Middle
  3. Same At All Points
  4. Found To Increase From One End To The Other

Answer: 3. Same At All Points

Question 11. To Convert An AC generator Into a DC generator

  1. Split-Ring Type Commutator Must Be Used
  2. Slip Rings And Brushes Must Be Used
  3. A Stronger Magnetic Field Has To Be Used
  4. A Rectangular Wire Loop Has To Be Used

Answer: 1. Split-Ring Type Commutator Must Be Used

Question 12. The Most Important Safety Method Used For Protecting Home Appliances From short-circuiting or Overloading Is

  1. Earthing
  2. Use Ofstabilizers
  3. Use Office
  4. Use Ofelectric Meter

Answer: 2. Use Of stabilizers

Question 13. Which ofthe following correctly describes the magnetic field near a long straight wire1?
Answer:

  1. The field consists of straight lines perpendicular to the wire.
  2. The field consists of straight lines parallel to the wire.
  3. The field consists of radial lines originating from the wire.
  4. The field consists of concentric circles centered on the wire.

Answer: 4. The magnetic field near a long straight wire the field consists of concentric circles centered on the wire.

Question 14. The phenomenon of electromagnetic induction is

  1. The Process of Charging A Body.
  2. The Process of Generating Magnetic Field Due To A Current Passing Through A Coil.
  3. Producing Induced Current In A Coil Due To Relative Motion Between A Magnet And The Coil.
  4. The Process Ofrotating A Coil Ofan Electric Motor.

Answer: 3. Electromagnetic induction produces induced current in a coil due to relative motion between a magnet and the coil.

Question 15. The device used for producing electric current is called a

  1. Generator
  2. Galvanometer
  3. Ammeter
  4. Motor

Answer: 1. A generator is used for producing electric current.

Question 16. The essential difference between an AC generator and a DC generator is that

  1. AC generator has an electromagnet while a DC generator has a permanent magnet.
  2. DC generator will generate a higher voltage.
  3. AC generator will generate a higher voltage.
  4. AC generator has slip rings while the DC generator has a commutator.

Answer: 2. The AC generator has slip rings while the DC generator has a commutator.

Question 17. At the time short circuit, the current in the circuit

  1. Reduces Substantially
  2. Does Not Change
  3. Increase Heavily
  4. Vary Continuously

Answer: 3. At The Time Of a Short Circuit The current in the circuit increases greatly

Question 18. State whether the following statements are true or false.

  1. An electric motor converts mechanical energy into electrical energy.
  2. An electric generator works on the principle of electromagnetic induction.
  3. The field at the center of the long circular coil carrying current will be parallel straight
    lines.
  4. A wire with green insulation is usually the live wire ofan electric supply.

Answer: 1. False. It converts electrical energy into mechanical energy.

  1. True.
  2. True. The field is almost uniform at the center of the coil.
  3. False. The ware with green insulation is usually the live wire.

Question 19. What happens to the deflection of the compass needle placed at a point near current carrying straight conductor:

  1. If the current is increased?
  2. If the direction of the current in the conductor is changed (reversed)?
  3. If the compass is moved away from the conductor?

Answer:

  1. The deflection of the compass needle increases.
  2. The direction of deflection in the compass needle changes.
  3. The deflection of the compass needle decreases.

Question 20. A coil of insulated wire is connected to a galvanometer. Explain what happens if a bar magnet with its north pole towards one face ofthe coil is:

  1. Moved Quickly Towards The Coil,
  2. Kept Stationary Inside The Coil, And
  3. Moved Quick Away From The Coil?

Answer: The increasing magnetic field induces current in the coil as a result of which the galvanometer shows momentary deflection (say towards the right).

No change in a magnetic field, no induced current, and deflection zero.

The magnetic field decreases, the induced current is produced in the coil and the galvanometer shows momentary deflection in the opposite direction (say towards the left).

Question 21. Which of the following properties of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

  1. Mass
  2. Speed
  3. Velocity
  4. Momentum

Answer: The correct options are (c) and (d). The magnetic force acts perpendicular to the direction of motion of the proton. It does not change its mass and speed but changes its direction of motion. So both velocity and momentum get changed.

Question 22. A positively charged particle (alpha-particle) projected towards the west is deflected towards the north by a magnetic field. The direction of the magnetic field is

  1. Towards South
  2. Towards East
  3. Downward
  4. Upward

Answer: The correct option is 4. This is by Fleming’s left-hand rule

Question 23. Choose the correct option.
Answer: A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

  1. Two Revolutions
  2. One Revolution
  3. Half revolution
  4. One-Fourth Revolution

Answer: The correct option is (b).

Question 24. Name two safety measures commonly used in electric circuits and appliances.

Answer:

  1. Earthing
  2. Electric fuse

CBSE Class 10 Science Chapter 14 Sources Of Energy Short Answer Questions

CBSE Chapter 14 Sources Of Energy Short Question And Answers

Question 1. If you could use any source of energy for heating your food, which one would you use and why?
Answer: We would prefer to use cooking gas like LPG or PNG or electricity. It fulfils many ofthe criteria of a good fuel, most importantly its ignition temperature, good calorific value and non-pollution characteristics.

Question 2. What are the disadvantages of fossil fuels?
Answer: There are the following disadvantages of fossil fuels like coal and petroleum:

  1. Burning of coal or petroleum causes air pollution.
  2. Acidic oxides like oxides of carbon, nitrogen and sulphur are released on burning fossil fuels. These oxides lead to acid rains, which affect our water and soil resources.
  3. Carbon dioxide gas also causes a greenhouse effect in the atmosphere.
  4. Fossil fuels are non-renewable sources of energy.

Question 3. Why are we looking at alternate sources of energy?
Answer: Fossil fuels are non-renewable sources of energy and their reserves are limited. Besides, these cause lots of pollution. Hence, we need to conserve them. If we continue consuming these sources at the same rate as presently, we may soon run out of energy. To avoid such a situation we are looking at alternate sources of energy.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 4. How has the traditional use of wind and water energy been modified for our convenience?
Answer: To use the kinetic energy of flowing water or the potential energy of water at a height, large dams have been built in hilly regions to store huge amounts of water at a height.

The stored water from the level in the dam is carried through pipes to the turbine at the bottom of the dam and runs the hydropower plant. Similarly, the wind energy is used to generate electricity. For this purpose, the rotatory motion of the windmill is used to turn the turbine ofthe electric generator.

CBSE Class 10 Science Chapter 14 Sources Of Energy.

Question 5. What kind of mirror—concave, convex or plain—would be best suited for use in a solar cooker? Why?
Answer: Large-size concave mirrors are best suited for use in a solar cooker because they focus large amounts of solar radiation on a small surface area so the temperature will rise quickly and appreciably.

Question 6. What are the limitations ofthe energy that can be obtained from the oceans?
Answer: Energy from the oceans can be obtained in the form of tidal energy, wave energy and ocean thermal energy.

But these energy sources suffer from the following limitations:

  1. There are very few locations where dams to utilise tidal energy can be built.
  2. The cost of installation of powerhouses is extremely high and the efficiency of plants is comparatively small.
  3. Power plants built in oceans or at seashores will need continuous maintenance as the chances of corrosion are extremely high.

Question 7. What is geothermal energy?
Answer: Geothermal energy is the heat energy present inside the earth in certain regions called ‘hot spots’. Due to geological changes, molten rocks formed in the deeper hot regions of Earth’s crust are pushed upwards and are trapped in hot spots. When underground water comes in contact with the hot spot, steam is generated. This steam is the source of geothermal energy.

Question 8. What are the advantages of nuclear energy?
Answer: The main advantages of nuclear energy are as follows:

  1. For a given mass of fuel consumed the amount of energy released is extraordinarily large.
  2. Nuclear power plants can be designed and constructed at any convenient place.
  3. If proper precautions are taken while running nuclear power plants, a major fraction of energy needed can be obtained from nuclear energy sources which is being done by many developed countries.

Question 9. Can any source of energy be pollution-free? Why or why not?
Answer: We shall call a source of energy to be pollution-free if neither it causes any pollution during its actual operation nor there is any pollution during assembly of devices utilising that source of energy. As an example, the solar cell is a clean and pollution-free source by itself but assembly of solar cell devices may have caused some pollution.

Question 10. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Answer: Hydrogen can be considered a cleaner fuel because its burning produces only water vapour which is non-polluting. However, due to the explosive nature ofhydrogen, its storage and transportation are difficult.

Question 11. Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer: Solar energy, wind energy, ocean energy etc., are renewable sources of energy for the following reasons:

  1. These forms of energy are available in plenty of our natural environment in the form of continuous currents of energy.
  2. These energy sources will not be depleted so long as the present solar system exists.

Question 12. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Answer: Coal and petroleum are two exhaustible sources of energy. These fuels were formed millions of years ago and there are only limited reserves. If we continue To Use Them As At Present, These Reserves Will Be Exhausted Soon.

Question 13. Compare and contrast fossil fuels and the sun as direct sources of energy.
Answer: The comparison between fossil fuels and the sun as a direct source of energy is as follows:

CBSE Class 10 Science Chapter 14 Sources Of Energy Comparison between fossil fuels and sun

Question 14. Compare and contrast biomass and hydroelectricity as sources of energy.
Answer: Differences between Biomass and Hydroelectricity:

CBSE Class 10 Science Chapter 14 Sources Of Energy Comparison between fossil fuels and sun

Question 15. What are the limitations of extracting energy from:

  1. The Wind1?
  2. Waves?
  3. Tides?

Answer:

Limitations of extracting energy from the wind are as given below:

  1. Wind energy farms can be established at those places only, where the wind blows for the greater part of a year.
  2. For wind energy, the wind speed should be higher than 15 km/h.
  3. A wind farm requires a large area and the initial cost of establishment of a farm is high.
  4. It requires a high level of maintenance because the tower and blades are exposed to rain, sun, storm, etc.
  5. It requires a backup with batteries for periods when there is no wind.
  6. Limitations of extracting wave energy are as follows:
  7. Wave energy can be harnessed by trapping the sea waves in a dam. Only very few suitable sites exist where dams can be constructed.
  8. It is not a continuous and reliable source of energy.
  9. It is extremely costly, cumbersome and difficult to maintain a power unit based on wave energy on a sustained basis.
  10. The limitations of extracting tidal energy are the same as for wave energy.

Question 16. On what basis would you classify energy sources as

  1. Renewable And Non-Renewable?
  2. Exhaustible And Inexhaustible?
  3. Are the options given in and the same?

Answer: Renewable sources of energy are those sources which can be regenerated again. Nonrenewable sources of energy are those sources which would get depleted someday and cannot be regenerated.

  1. Exhaustible sources of energy are those which will get depleted someday and cannot be regenerated. Inexhaustible sources of energy are those which can be regenerated again due to some continuing or repetitive currents of energy.
  2. Options are given in and are the same. A non-renewable source is an exhaustible source. A renewable energy source is an inexhaustible source.

Question 17. What are the qualities ofan ideal source of energy?
Answer: The qualities of an ideal source of energy are as given below:

  1. It should be an easily accessible, inexhaustible, renewable source of energy and the cost of harnessing energy should be reasonably small.
  2. The energy obtained from the source should be easily stored and transferred from one place to another place.
  3. The energy source should not cause directly or indirectly any sort of pollution or degradation of the environment.
  4. The technology for harnessing energy from a given source should be easily available, cheap and efficient.

Question 18. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Answer: Advantages of a solar cooker

  1. There is no cost of fuel.
  2. It is environment friendly and there is no residue like ash etc.
  3. Cooking is hygienic and nutritious.
  4. Disadvantages of a solar cooker
  5. The cooking is slow. It takes 2-3 hours to attain a temperature of100°C-140°C on a sunny day.
  6. It does not work on a cloudy day.

Question 19. What are the environmental consequences of the increasing energy demand? What steps would you suggest to reduce energy consumption?
Answer: Ronment in some way or the other. Either it would cause more pollution or cause environmental damage. Development and consumption of energy would go together. Therefore we should concentrate more on finding better and alternative sources of energy.

When looking for alternative sources, the following points should be kept in mind:

  1. Ease and cost of extracting energy from the source,
  2. The efficiency of the available technology.
  3. Environmental impact of using that source

Answer:

Question 20. Define fuel. List any two characteristics that you would look for in a good fuel.
Answer: Fuel is a source of energy that we choose for doing some work.

  1. Amount of ofheat released by it on burning per unit mass
  2. Easy storage and transportation
  3. Economical
  4. Pollution-free.

Question 21. The waste materials collected from a market complex are scrap paper, thermocol, vegetable waste, tin cans and glass bottles. Which ofthese can be used for producing biogas? Mention three advantages of converting these into biogas rather than burning them.
Answer: Scrap paper and vegetables can be used to produce biogas. Converting these into biogas has the following advantages:

  1. It produces cheap and valuable fuel for which there is a great demand.
  2. It utilises those substances which would, otherwise be wasted and, require space for its safe dumping.
  3. If this waste is left as such then it will be decomposed by microorganisms. This
    results in the release of harmful gases which increases environmental pollution.

Question 22. Compare the advantages of generating energy from biomass to getting it from hydropower plants.
Answer:

CBSE Class 10 Science Chapter 14 Sources Of Energy The Advantages of generating energy

Question 23. What do you mean by a clean fuel? Is an absolute clean fuel available?
Answer: A clean fuel is that which does not cause environmental damage when used to produce energy.

No fuel is clean. Some environmental damage is caused directly or indirectly by the fuel. We can only call one source less or more cleaner than the others.

Question 24. Mention the advantages and limitations of wind energy.
Answer: Advantages:

  1. It IH used to propel sailboats.
  2. It is used to drive windmills which further operate water lifting, pumps and flourmills.
  3. Aeroplanes use this energy for their upward and downward movements
  4. It is used for flying engineless aeroplanes called gliders and for generating electricity.
  5. It is free of cost and does not cause any pollution.

Limitations:

  1. It is not available at all times.
  2. It requires a very large area of land.
  3. It is not possible to have a windmill everywhere, as to run it, the minimum wind
    speed of 15 km/h is required.

Question 25. Why is biogas plant considered to a be boon to the farmers? Give reason.
Answer: Biogas plants are considered to be a boon to the farmers because farmers can get clean fuel which does not produce any kind of smoke and pollution as compared to dried dung cakes.

Question 26. List any four reasons why we need to look for alternate sources ofenergy.
Answer: Pollution due to fossil fuels, exhausting fuel reserves, increasing need, replenishment is not easy.

Question 27. Explain why obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions. Give two reasons.
Answer: Obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions because:

  1. For a given mass, the energy released from nuclear fusion is much larger than the energy released from nuclear fission.
  2. Nuclear waste in nuclear fission is radioactive. Its disposal is a big challenge. There is no such difficulty in nuclear fusion.

Question 28. Why is tidal energy not likely to be a potential source of energy?
Answer: The harnessing of tidal energy poses many problems. The rise and fall of water during tides is not high enough to generate electricity on a large scale. There are very few sites that are suitable for building dams. It is for these reasons that tidal energy is not likely to be a major source of energy.

Question 29. “Electricity generated by the water stored in a dam can be considered to be another form of solar energy.” Explain describing the series of energy transformations in sequence taking place during the process.
Answer: Given below is the sequence of energy transformations that take place in the generation of electricity from the water stored in a dam.

Solar energy changes into potential energy (PE) of water vapour rising in the atmosphere, during the evaporation of water from rivers, seas, oceans and other water masses. These water vapours form clouds and cover mountains with snow.

  1. When clouds burst into rain or the snow melts, their PE changes into kinetic energy of water flowing into streams and rivers.
  2. When this flowing water is stored in a dam, its KE changes into PE.
  3. When water is released from the dam, its PE once again changes into KE.
  4. The KE of water coming out of the dam moves turbines which generate electricity.
  5. Thus, it is the solar energy which changes into electricity.

Question 30. What is natural gas? How is it formed?
Answer: Natural gas is a naturally occurring mixture of methane (approx. 85%), ethane (10%), propane (3%), and butane (2%). Other non-combustible gases like CO2, N2 and O2 may also be present in the mixture.

Natural gas is formed by the action of heat, pressure and microorganisms on buried organic matter over millions of years.

Question 31. Give two advantages ofsmokeless chulha over traditional chulha.
Answer:

  1. It has more efficiency and produces less smoke
  2. It is scientifically designed and consumes less fuel.
  3. The complete combustion of fuel takes place in it and it has a tall chimney.

Question 32. Justify the statement ‘Hydrogen is a cleaner and better fuel than CNG’.
Answer: Yes, it is a cleaner fuel because on burning, hydrogen produces only water vapour which is non-polluting. Although it is not used in everyday life due to its explosive nature, storage and transportation problems.

Question 33. What is nuclear waste? What are the hazards of nuclear waste to living beings? How is nuclear waste disposed of?
Answer: The discarded material of the nuclear industry is called nuclear waste such as remains in the containers which are used to handle radioactive substances or radioactive products of nuclear reactions.

  1. The waste material more often possesses radioactivity which emits particles capable of damaging man, animal and plant tissues.
  2. Nuclear wastes cannot be destroyed by chemical or other methods. These have to be buried deep under the earth.

Question 34. A student constructed a box-type solar cooker. He found that it was not working efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker?
Answer: He might not have painted the box black from the inside.

  1. He might not have placed the blackened sheet in the insulated part of the solar cooker.
  2. He might not have attached the reflector at the right angle.
  3. He might not have covered his box with a thick glass sheet. He might have used a thin glass sheet.

Question 35. Why is a floating gas holder-type biogas plant considered less advantageous than a fixed dome-type biogas plant? Give reasons.
Answer: Floating gas holder type biogas plant is considered less advantageous because:

  1. A floating gas holder type biogas plant is costly as it is made of steel.
  2. Gas can leak through it either due to defects in welding or due to corrosion of steel.
  3. It has to be repaired and painted frequently which increases its maintenance cost.

Question 36. Why is charcoal considered to be a better fuel than wood? What are the disadvantages of converting wood into charcoal?
Answer: Charcoal is considered as a better fuel than wood because:

  1. Charcoal burns easily without producing smoke.
  2. It gives twice as much heat as given by the same mass of wood.
  3. The disadvantage of converting wood into charcoal is that during destructive distillation of 1 kg of wood only 0.25 kg of charcoal is obtained.
  4. In other words, the conversion is expensive; hence charcoal is an expensive fuel.

Question 37. Why can wind energy farms be established only at specific locations? Give reasons to support Your Answer
Answer: Wind energy farms can be set up only in locations:

  1. Where the wind blows for the greater part of the year.
  2. Where the wind is strong and steady and has a speed of about 16 km h-1.
  3. Where large free space is available.
  4. Since these conditions cannot be satisfied everywhere, therefore, wind energy farms can be set up only in specific locations.

Question 38. Why is it not possible to make use of solar cells to meet all our energy needs? State at least three reasons to support your answer.
Answer: High cost of installation.

  1. Limited availability of special-grade silicon to make solar cells.
  2. Unavailability of an efficient system to store electrical energy generated by solar panels.

Question 39. What are thermal power plants? Give a demonstration of how thermal energy can be converted into electrical energy.
Answer: Thermal power plants convert heat energy into electrical energy. In thermal power plants, fuels are burnt to heat water to produce steam which is designed to run the turbine to generate electricity. The class can be demonstrated as follows:

What are thermal power plants

Take a tennis ball and make three silts into it. Fit three small fins of a metal sheet into these slits. Fix the tennis ball on an axle as shown so that the ball has a free rotation.

Now connect this axle to a bulb through a dynamo. Direct a jet of steam from a pressure cooker onto to fins of the ball. Soon the bulb will start glowing. It will glow till the ball is rotating with the help of steam.

Question 40. Biomass has been used as fuel since ancient times, how has it been modified to function as a more efficient fuel in the recent past?
Answer: Coal and petroleum.

Yes, it is a cleaner fuel because on burning only water vapour is produced, which is non-polluting but due to the explosive nature of hydrogen storage and transportation is difficult.

Question 41. State the principle of a reflector-type solar cooker. How is this type of solar cooker different from a box type of solar cooker?
Answer: Reflector-type solar cooker: In this solar cooker, a concave reflector or parabolic reflector is used. It concentrates the solar energy in a small region called focus and therefore quite high temperature can be produced.

This way is different from box-type solar cookers because here food materials requiring strong heating can also be cooked. It can be used for baking and frying also.

Question 42. With the help of a diagram, explain how the design of a box type of solar cooker ensures minimum loss ofheat from its inside.
Answer: The box of the solar cooker is made of-conducting material, for example, plastic or fibreglass with thick inner walls. It is covered with a glass sheet which prevents loss of longer wavelength infrared radiations from inside to outside.

NCERT Solutions For Class 10 Science Chapter 14 Sources Of Energy Solar cooker

Question 43. Write the composition and source of LPG. Although liquefied gas is present in the cylinder, how does it appear as a gas in the burner?
Answer: LPG contains Butane (main), Propane and Ethane. It occurs over petroleum. Some wells contain only petroleum gas.

It is present in liquid form in the cylinder because it is filled at very high pressure, therefore, it liquefies. But when it comes out of the cylinder, the pressure is released and it appears as a gas in the burner.

Question 44. State four characteristics ofan ideal fuel.
Answer: It should be cheap and easily available.

  1. It should have a high calorific value and should burn smoothly.
  2. It should have a moderate ignition temperature and should be easy to store, handle
    and transport.
  3. It should not leave any residue and should not produce smoke and harmful products.

Question 45. Give the disadvantages of constructing big dams across the river. How does the construction of dams across the river get linked with the production of greenhouse gases?
Answer: Large areas of agricultural land and the human population get submerged.

The problem of rehabilitation of displaced people.

The vegetation which is submerged rots under anaerobic conditions, giving a large amount of methane which is a greenhouse gas.

Question 46. Electricity generated by the water stored in a dam can be considered to be another form of solar energy. Describe the series of energy transformations in sequence during the process.
Answer: CBSE Class 10 Science Chapter 14 Sources Of Energy Electricity generated by the water stored

Question 47. How can the pollution caused by fossil fuels be reduced?
Answer: The pollution caused by fossil fuels can somewhat be reduced by:

Increasing the efficiency of the combustion process using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

Question 48. What is a thermal powerplant? Where is preferably situated?
Answer: In thermal power plants, fossil fuel is burnt to convert water into steam which further rotates the turbines to produce electricity.

Such plants are preferably located near coal mines or oil fields and away from habitats. It is easier to transport electricity than to transport coal or petroleum.

Question 49. A student constructed a model of a box-type solar cooker. He used a transparent plastic sheet to cover the open face of the box. He found that this cooker does not function well. What could be the possible drawbacks of his model? List any four drawbacks.
Answer: He may not have used:

  1. Black painted aluminium sheet.
  2. Black cooking vessel to absorb heat radiation.
  3. Glass sheet, which prevents the escape of heat radiation from the box instead of plastic sheet.
  4. Mirror plate which reflects the sunlight to fall on the glass sheet.

Question 50. Why is there a need to harness non-conventional sources ofenergy? Give two main reasons.
Answer: Our energy demand is increasing to improve the quality of life and population growth.

  • Fossil fuels are limited.

Question 51. Write two different ways of harnessing energy from the ocean.
Answer: The two different ways of harnessing energy from the ocean are as follows:

  1. Tidal energy—the energy derived from rising and falling ocean tides is called tidal energy.
  2. Ocean thermal energy—solar energy stored in the oceans in heat is known
    as ocean thermal energy.

Question 52. What steps would you suggest to minimise environmental pollution caused by the burning of fossil fuels?
Answer:

  1. Use of smokeless appliances
  2. Afforestation

Question 53. What is the role of the plane mirror and a glass sheet in a solar cooker?
Answer: A plane mirror acts as a reflector and a glass sheet results in a greenhouse effect.

Question 54. Mention three advantages of solar cells.
Answer: Solar cells have no moving parts.

  1. Requires little maintenance.
  2. They can be set up in the remote areas.

Question 55. What is biomass? What can be done to obtain bio-energy using biomass?
Answer: The waste material of living things and dead parts of plants and animals is called biomass.

  1. It has been a traditional source of energy, e.g. wood, crop residue, and bagasse cow-dung cake are used as fuels for domestic as well as industrial uses.
  2. Bio-energy in the form of biogas can be produced from biomass by the decomposition in the absence of air. Biomass such as wood, cow dung etc., is directly used as fuel.

Question 56. What are the limitations of obtaining energy from wind?
Answer: Because wind energy is erratic energy cannot be harnessed continuously.

Large areas are required for wind forms.

Question 57. Suggest any three ways to contribute to saving LPG/CNG at home.
Answer: Soak dais, and rice in water before cooking, so that it takes less time and fuel for cooking.

  1. Use a pressure cooker most of the time.
  2. Cover the lid of the container while cooking.

Question 58. A student constructed a box-type solar cooker. He found that it was not working efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker?
Answer: He might not have painted the box black from the inside.

  1. He might not have placed the blackened sheet in the insulated part of the solar cooker.
  2. He might not have attached the reflector at the right angle.
  3. He might not have covered his box with a thick glass sheet. He might have used a thin glass sheet.

Question 59. A student wants to design a car which runs on any alternative source ofenergy. Suggest any two sources ofenergy and give their advantages.
Answer: Solar cell panels can be installed on the top of the roof. It can convert solar energy into electrical energy.

Use water as a fuel which can split into H2 and 02 gas. H2 gas produced is used to run the engine.

Question 60. A person ‘A’ rolled up the glasses of his black car and parked it in the sun for one hour. Another person ‘B’rolled up the glasses of a white car and parked in the sun for one hour. In which car is the temperature higher and why?
Answer: Black car; the black colour is a good absorber ofheat and glass causes the greenhouse effect.

Question 61. The waste materials collected from a market complex are scrap paper, thermocol, vegetable waste, tin cans and glass bottles. Which ofthese can be used for producing biogas? Mention three advantages of converting these into biogas rather than burning them.
Answer: Scrap paper and vegetables can be used to produce biogas. Converting these into biogas has the following advantages:

  1. It produces cheap and valuable fuel for which there is a great demand.
  2. It utilizes those substances which would, otherwise be wasted and, require space for their safe dumping.
  3. If this waste is left as such then it will be decomposed by microorganisms. This results in the release of harmful gases which increases environmental pollution.

Question 62. “A biogas plant solves the fuel as well as environmental problems”. Discuss.
Answer: Biogas is an ideal fuel, as:

  1. It has a high calorific value.
  2. It does not produce smoke.
  3. It has a moderate ignition temperature.
  4. It does not form harmful products.
  5. It is very cheap and can be made available easily.

Because of the above-mentioned characteristics:

  1. Biogas acts as an excellent fuel and hence solves the fuel problem.
  2. Biogas does not create air pollution, therefore, it solves environmental problems also.
  3. Biogas also prevents water pollution.

Sources Of Energy Multiple Choice Questions

Question 1. Which of the following is a non-renewable source of energy?

  1. Wood
  2. Sun
  3. Fossil fuels
  4. Wind

Answer: 3. Fossil fuels

Question 2. Acid, rain happens because.

  1. Sun leads to the heating of the upper layer of the atmosphere
  2. Burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere
  3. Electrical charges are produced due to friction among clouds
  4. Earth’s atmosphere contains acids

Answer: 2. Burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere

Question 3. Fuel used in thermal power plants is

  1. Water
  2. Uranium
  3. Biomass
  4. Fossil fuels

Answer: 4. Fossil fuels

Question 4. In a hydropower plant

  1. Potential energy possessed by stored water is converted into electricity
  2. Kinetic energy possessed by stored water is converted into potential energy
  3. Electricity is extracted from water
  4. Water is converted into steam to produce electricity

Answer: 1. Potential energy possessed by stored water is converted into electricity

Question 5. Which is the ultimate source of energy?

  1. Water
  2. Sun
  3. Uranium
  4. Fossil fuels

Answer: 2. Sun

Question 6. Which one of the following forms of energy leads to the least environmental pollution in the process of harnessing and utilisation?

  1. Nuclear energy
  2. Thermal energy
  3. Solar energy
  4. Geothermal energy

Answer: 3. Solar energy

Question 7. Ocean thermal energy is due to

  1. Energy Stored By Waves In The Ocean
  2. Temperature Difference At Different Levels In The Ocean
  3. Pressure Difference At Different Levels In The Ocean
  4. Tides Arising Out In The Ocean

Answer: 2. Temperature Difference At Different Levels In The Ocean

Question 8. The major problem in harnessing nuclear energy is how to

  1. Split Nuclei?
  2. Sustain The Reaction?
  3. Dispose Of Spent Fuel Safely?
  4. Convert Nuclear Energy Into Electrical Energy?

Answer: 3. Convert Nuclear Energy Into Electrical Energy?

Question 9. Which part of the solar cooker is responsible for the greenhouse effect?

  1. Coating with black colour inside the box
  2. Mirror
  3. Glass sheet
  4. The outer cover of the solar cooker

Answer: 3. Outer cover of the solar cooker

Question 10. The main constituent of biogas is

  1. Methane
  2. Carbon Dioxide
  3. Hydrogen
  4. Hydrogen Sulphide

Answer: 1. Methane

Question 11. The power generated in a windmill is greater in the rainy season since damp air would mean more air mass hitting the blades

  1. Depends On The Height Of The Tower
  2. Depends On Wind Velocity
  3. Can Be Increased By Planting Tall Trees Close To The Tower

Answer: 3. Can Be Increased By Planting Tall Trees Close To The Tower

Question 12. Choose the correct statement

  1. Sun can be taken as an inexhaustible source of energy
  2. There is infinite storage of fossil fuel inside the earth
  3. Hydro and wind energy plants are non-polluting sources of energy
  4. Waste from a nuclear power plant can be easily disposed off

Answer: 1. The Sun can be taken as an inexhaustible source of energy

Question 13. In a hydroelectric power plant, more electrical power can be generated if water falls from a greater height because

  1. Its Temperature Increases
  2. Larger Amount Of Potential Energy Is Converted Into Kinetic Energy
  3. The Electricity Content Of Water Increases With Height
  4. More Water Molecules Dissociate Into Ions

Answer: 2. Larger Amount Of Potential Energy Is Converted Into Kinetic Energy

Question 14. Choose the incorrect statement regarding wind power

  1. It is expected to harness wind power to a minimum in open space
  2. The potential energy content of wind blowing at high altitudes is the source of wind power
  3. Wind hitting the blades of a windmill causes them to rotate. The rotation thus achieved can be utilised further
  4. One possible method of utilising the energy of the rotational motion of the blades of a windmill is to run the turbine of an electric generator.

Answer: 2. The potential energy content of wind blowing at high altitudes is the source of wind power

Question 15. Choose the incorrect statement

  1. We are encouraged to plant more trees to ensure a clean environment and also provide biomass fuel
  2. Gobar gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
  3. The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash
  4. Biomass is a renewable source of energy

Answer: 3. The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash.

Question 16. A solar water heater cannot be used to get hot water on

  1. A Sunny Day.
  2. A Hot Day.
  3. A Cloudy Day.
  4. A Windy Day.

Answer: 2. A cloudy day (because on a cloudy day, no radiations from the sun are incidentÿn the solar water heater. Hence, it cannot be used to get hot water).

Question 17. Which of the following is not an example of a biomass energy source?

  1. Wood
  2. Gobar-Gas
  3. Nuclear Energy
  4. Coal.

Answer: 3. Nuclear energy.

Question 18. Most ofthe sources of energy we use represent stored solar energy. Which ofthe following is not ultimately derived from the Sun’s energy?

  1. Geothermal energy
  2. Nuclear energy
  3. Wind energy
  4. Biomass

Answer: 1. Geothermal energy.

CBSE Class 10 Science Chapter 11 Human Eye And Colorful World Very Short Answer Questions

Human Eye And Colourful World Very Short Answer Questions

Question 1. A person with a myopic eye cannot distinctly see objects beyond 1.2 m. What should be the type of corrective lens used to restore proper vision?
Answer: Diverging or concave lens.

Question 2. What are the far and near points of the human eye with normal vision?
Answer: For a human eye with normal vision, the far point is at infinity and the near is at 25 cm from the eye.

Question 3. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Answer: The child is suffering from myopia. He should use concave lenses of suitable focal length.

Question 4. What is astigmatism?
Answer: It is a defect in which a person cannot see in all directions equally well.

Question 5. Where does the greatest degree of refraction oflight occur in the eye?
Answer: At the cornea.

Question 6. A man wearingglassesatfocal length of +1 cannot see objects beyond 1 what is the defect in his eye?
Answer: Myopia.

Read and Learn More CBSE Class 10 Science Very Short Answer Questions

Question 7. What is the function of the choroid?
Answer: It, contains black pigments which avoid internal reflections within the eye.

Question 8. What happens to the lens and the ciliary muscles when you are looking at
Answer: The ciliary muscles contract and the lens becomes thick, i.e. its radius of curvature decreases.

Question 9. Define dispersion of white light.
Answer: The splitting of white light into seven colours on passing through a transparent medium, i.e. glass prism, is called dispersion of light.

Question 10. What is presbyopia?
Answer: It is a defect of vision due to which an old person cannot see nearby objects clearly due to loss of power of accommodation of the eye.

CBSE Class 10 Science Chapter 11 Human Eye And Colorful World

Question 11. Name a natural phenomenon which is caused by the dispersion of sunlight in the sky.
Answer: Formation of the rainbow.

Question 12. Give one cause of sightedness.
Answer: Increase the focal length of the eye lens.

Question 13. What would have been the colour ofthe earth’s sky if there were no atmosphere?
Answer: It would have been dark.

Question 14. State one function ofthe crystalline lens in the human eye.
Answer: It produces a real and inverted image of the object on the retina.

Question 15. Name the type of particles which act as a prism in the formation of the rainbow in the sky.
Answer: Water droplets are present in the atmosphere.

Question 16. Name two types of cells in the retina of the eye which respond to light.
Answer: Rods and cones.

Question 17. What is the Tyndall effect?
Answer: The scattering oflight by particles in its path is called the Tyndall effect.

Question 18. On what factor does the colour ofthe scattered light depend?
Answer: It depends on the size of the scattering particles.

Question 19. How is the sense of vision carried from the eye to the brain?
Answer: Through the optic nerve.

Question 20. What is an iris?
Answer: The coloured diaphragm between the cornea and lens.

Question 21. Why does the sky appear dark to astronauts?
Answer: For scattering oflight, particles are required since there are no particles in space the sky appears dark to an astronaut.

Question 22. Give one example of a phenomenon where the Tyndall effect can be observed.
Answer: When a beam of sunlight enters a dusty room through a window, its path becomes visible to us.

Question 23. Give an example of an optical phenomenon which occurs in nature due to atmospheric refraction.
Answer: Advanced sunrise and delayed sunset.

Question 24. A person suffering from an eye defect uses lenses of power -10. Name the defect he is suffering from and the nature of the lens used.
Answer: Myopia, concave lens.

Question 25. Name the condition resulting due to the eye lens becoming cloudy.
Answer: Cataract.

Question 26. Name the two phenomena involved in the formation of a rainbow.
Answer: 1. Dispersion

Question 27. A person is advised to wear spectacles with concave lenses. What types of defect of the vision is he suffering from?
Answer: Myopia or short-sightedness.

Question 28. What is a blind spot?
Answer: A point at which the optic nerve leaves the eye.

Question 29. Why is blind spot so-called?
Answer: An image formed at this point is not sent to the brain.

Question 30. What is the role of the pupil in the human eye?
Answer: The pupil regulates and controls the amount oflight entering the eye.

Question 31. Which colour of white light suffers the least deviation and maximum deviation when a beam of white light passes through a glass prism?

  1. Red
  2. Violet

Answer: 2. Total internal reflection

Question 32. What is the range of vision for a normal human eye?
Answer: It is 25 cm to infinity.

Question 33. Name the part of the human eye that helps in changing the focal length of the eye lens.
Answer: Ciliary muscles.

Question 34. Does a beam of white light give a spectrum on passing through a hollow prism?
Answer: No, because dispersion oflight cannot occur through a hollow prism containing prism.

Question 35. Can an observer see a rainbow on the moon1?
Answer: No, there is no atmosphere on the moon.

Question 36. Is the position of a star as seen by us in its true position? Justify your answer.
Answer: No, light from stars undergoes atmospheric refraction which occurs in the medium of gradually changing refractive index.

Question 37. Is the position of a star as seen by us its true position? Justify your answer.
Answer: No. Light from stars undergoes atmospheric refraction which occurs in the medium of gradually changing refractive index.

Question 38. How are we able to see nearby and also the distant objects?
Answer: By use of bifocal length. It enables us to see both distant and nearby objects.

Question 39. Explain why the planets do not twinkle.
Answer: Planets being of larger size can be taken as a collection of large numbers of sized objects/sources oflight, which nullify the twinkling effect of each other.

Question 40. We see advertisements for eye donations on television or in newspapers. Write the importance of such advertisements.
Answer: Such advertisements motivate people to pledge their eyes for donation after death. They also spread awareness about eye donation amongst the people. They dispel myths and misconceptions associated with eye donation.

Question 41. No rainbow could be observed from the surface of the moon by the astronaut. Give reason.
Answer: The moon does not have any atmosphere and no water droplets are present. Hence, no dispersion oflight is possible. Therefore, astronauts cannot see a rainbow from the moon.

Question 42. What are rods and cones?
Answer: These are light-sensitive cells present in the retina. Rods control the intensity of light, while cones control the colour perceptions.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants

Getting To Know Plants

There is a large number of plants growing around us. These differ in shape, size, color, and height. Some plants are small, some are very big and some are just patches of green on the soil.

Some plants have green leaves, while B some have reddish ones. Similarly, some plants have huge red flowers, while, some have tiny blue ones.

Some unwanted plants grow in crop fields, lawns, or in pots. These are known as weeds, for example, bermuda grass. They all are living entities, but are different from animals. They grow on soil and remain fixed in one place.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants

Types Of Plant

According to their size and nature of stem, plants are classified into the following three categories

  1. Herbs These are small plants with green, soft and tender stems. They do not have many branches, for example, bathua, tomato, paddy, grass, mint, etc.
  2. Shrubs These are bigger than herbs. Their stem is hard, but not very thick and has branches at the base of the stem, for example, jasmine, lemon, rose, tulsi, etc.
  3. Trees These are very tall and have hard and thick brown stems. The stems have branches on the upper part of the plants, for example, neem, mango, peepal, etc.

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CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants Types Of Plants

There are some plants which are different from herbs, shrubs and trees. These are called creepers and climbers.

Creepers are plants that have thin, long and weak stems which cannot stand upright but spread on the ground, for example, strawberries, pumpkins, watermelons, etc.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants Creepers

Climbers are plants having soft, green and weak stems which cannot stand upright just like the creepers, but readily climb up taking support from nearby objects or trees, for example, bitter gourd, grapevines, bean stalks, etc.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants Climbers

Science Insight A climber plan, has special organs called tendrils for climbing. Some of these have stem tendrils whereas others have leaf tendrils.

Parts Of A Plant

A plant is divided into different parts, i.e. stem, leaves, roots, etc. Each part performs a specific function.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants Parts Of A Plant

Stem

It is the aerial part of the plant which bears branches, flowers, buds, leaves and fruits. It may be green, hard or woody.

Functions Of Stem

It performs the following functions

  1. It helps in the upward movement of water and minerals from roots to different parts of the plants.
  2. The stem also conducts food from leaves to various plant parts through narrow tubes present inside it.
  3. Some stems get modified into various other forms in different plants to perform special functions, like in potato, onion and ginger, the stem is underground and modified to store food.

Leaf

It is a thin, flat and green part of the plant. Leaves of different plants have different shapes and sizes.

Parts of a Leaf

A leaf has the following parts

  1. Petiole (leafstalk) It is a thin stalk by which the leaf is attached to the stem.
  2. Lamina (leaf blade) It is the broad, green flattened part of a leaf. There are several small, thin lines running across the lamina called veins the central vein or the main vein of the leaf is called Madrid.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants The Parts Of A Leaf

Science Insight A leaf without a petiole is called a sessile leaf. In such plants, the leaves are attached directly to the plant stem.

Leaf Venation

The arrangement of veins in the leaf lamina is called leaf venation. There are two types of venation seen in different plants.

  1. Reticulate Venation In this type of venation, veins are arranged in a net-like pattern on both sides of the midrib. This type of venation is found in peas, neem, peepal, tulsi, mustard, sunflower, orange, guava, rose etc.
  2. Parallel Venation In this type of venation, veins are arranged parallel to each other and also along the midrib. This type of venation is found in certain plants like wheat, maize, onion, garlic, lily grass, etc.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants Leaf Venation

Functions of Leaves

They perform the following functions

  1. Leaves prepare their food in the presence of sunlight with the help of a green-coloured substance present in them. For this, they use water and carbon dioxide from the air. This process is called photosynthesis. Oxygen is given out in this process. The food prepared by leaves ultimately gets stored in different parts of the plant.
  2. They also help the plant to get rid of excess water by the process of transpiration.

Root

It is the underground, non-green part of the plant which remains below the ground, i.e. in soil.

Types of Root

There are mainly two types of roots

  1. Tap Root In some plants, there is one thick main root called tap root from which arises the smaller roots called lateral roots. Tap root grows vertically downwards into the soil and lateral roots spread in various directions. It is found in plants like peas, radishes, carrots, neem, mango, tulsi, marigolds, mustard and balsam.
  2. Fibrous RootIn some plants, there is no main root. All roots are similar and make a bushy appearance. This type of root is called fibrous root. It is found in plants like onion, lily, wheat, maize, grass and millet.

CBSE Notes For Class 6 Science Getting To Know Plants Types Of Roots

Functions Of Roots

They perform the following functions

  1. Roots anchor the plant to the soil. This prevents the plant from being pulled out easily or blown away by strong winds.
  2. They also absorb water and minerals from the soil. This helps in the manufacture of food by leaves.
  3. They hold the soil together. In this way, roots prevent the soil from being blown away by wind or washed away by water. This also helps in the conservation of soil.
  4. They help in the storage of food. Radish, carrot and turnip eaten by us are swollen tap roots. Similarly, Dahlia and sweet potatoes are fibrous roots which get modified to store food.

CBSE Notes For Class 6 Science Chapter 4 Getting To Know Plants

Flower

It is the reproductive structure of the plants. A flower has a stalk by which it is attached to the stem. Different types of plants bear different types of flowers, but the basic structure is almost the same in all plants (except a few).

Parts Of The Flower

A typical flower consists of four distinct parts or whorls, i.e. sepals, petals, stamens and pistils.

CBSE Notes For Class 6 Science Getting To Know Plants Parts Of Flowers

Sepals

The sepals form the outermost whorl of the flower. These are small, green leaf-like structures. They protect the flower in the bud stage.

Petals

They form the second whorl of flower lying inner to sepals. Petals are generally big and coloured structures. They vary in shape, size and structure in different plants. These are mostly bright in colour to attract insects, animals and even human beings.

Stamens

It is the third whorl of flower that lies inner to petals. Stamens are the male reproductive part of a flower and consist of two parts

Anther is the swollen long structure at the tip of each stamen. It contains a small powdery substance called pollen grains.

Filament is a long slender stalk-like structure which supports the anther.

CBSE Notes For Class 6 Science Getting To Know Plants Stamnes

Pistil

  1. The innermost part of a flower is called a pistil. This is the female reproductive part of a flower.
  2. It consists of the following three parts
  3. Stigma is a slightly swollen part at the top of the style. It is a small, round and sticky part that traps the pollen grains.
  4. Style is a long, thin and slender stalk in the middle that is attached to the stigma.
  5. The ovary is the swollen part present at the lowermost portion. It contains many ovules (egg-like structures).

CBSE Notes For Class 6 Science Getting To Know Plants Parts Of A Pistill

Science Insight The fruits and seeds are formed from flowers by the process of pollination and fertilization.

Activity 1

Aim: To show that water moves up through the stem of a plant.

Materials Required: A glass filled with water, red ink, stem of balsam plant, sharp object/knife, dropper.

Procedure:

  1. Take a glass filled with one-third of water and add some drops of red to it using a dropper.
  2. Cut the base of the stem of the balsam plant (or any other herb) carefully using a knife and put it in the glass.
  3. Observe the plant the next day.

CBSE Notes For Class 6 Science Getting To Know Plants The Stem Of A Plant

Observation We will observe that the colour rises in the stem, i.e. some parts of the stem become red. If this is kept for a longer period, the colour will appear in the veins of the leaves also.

Conclusion This activity shows that the stem helps in the upward movement of water and minerals to leaves and other parts attached to the stem.

Activity 2

Aim: To make the impression of the leaf on a white paper.

Materials Required: A white sheet of paper, a pencil, and a leaf of any plant.

Procedure:

  1. Put a leafunder a white sheet of paper.
  2. Hold it in place and start rubbing your pencil tip gently over the portion ofthe paper covering the leaf, keeping the pencil tip sideways.

CBSE Notes For Class 6 Science Getting To Know Plants Taking An Impression Of A Leaf On Paper

Observation: We will get the impression with some lines, i.e. leaf impressions are seen on the sheet defining its shape, size and venation.

Conclusion: This activity shows that the impression ofthe leaf is similar to that of the original leaf.

Activity 3

Aim: To show transpiration in plants.

Materials Required: A healthy plant, two transparent polythene bags and thread.

Procedure:

  1. Take a well-watered, healthy plant that has been growing in the Sun.
  2. Enclose a leafy branch of the plant with one of the polythene covers and tic up its mouth with thread.
  3. Take the other polythene bag and tie up its mouth with thread. Keep it in the Sun just like the previous one
  4. After a few hours observe the inner surface of the covers.
  5. Remove the polythene bag after the activity

CBSE Notes For Class 6 Science Getting To Know Plants Experimental Set Up To Show Transpiration

Observation: We observe that after some time small droplets of water appear inside the polythene bag covering the leafy branch of the plant.

This is due to the loss of water from the leaves which occurs by the process known as transpiration. Water droplets do not appear inside the empty polythene cover since the plant is absent.

Conclusion: This activity shows that transpiration is performed by the leaves.

Activity 4

Aim: To show that a leaf produces starch as a result of photosynthesis.

Materials Required: A leaf, spirit, a beaker, test tube, tripod stand, burner, water, iodine solution, dropper and watch glass.

Procedure:

  1. Take a test tube and put a leaf in it.
  2. Pour spirit into the test tube, so that the leaf gets completely immersed in it,
  3. Now, place this test tube in a beaker half-filled with water.
  4. Heat the beaker till all the green colour from the leaf comes out into the spirit in the test tube.
  5. Take out the leaf carefully and wash it with water.
  6. Place the leaf in a watch glass and pour iodine solution over it using a dropper.

CBSE Notes For Class 6 Science Getting To Know Plants To show that leafproduces starch as a result of Photosynthesis

Observation: The leaf turns blue-black showing the presence of starch in it.

Conclusion: This activity shows that leaves contain starch which is the product of photosynthesis.

Activity 5

Aim: To test that roots are essential for the plant.

Materials Required: Two pots, some soil, a blade or a pair of scissors, khurpi (for digging) and water.

Procedure:

  1. Select two plants ofthe same kind from an open ground.
  2. Dig them out with roots, taking care that roots do not break.
  3. Place one ofthe plants in pot A.
  4. Cut off the roots from the other plant, and place this plant in pot B.
  5. Water them regularly
  6. Observe both plants after a week.

CBSE Notes For Class 6 Science Getting To Know Plants Plant with and without roots

Observation: We will observe that the plant with roots planted in pot A is healthy and alive, while the plant without roots in pot B is wilted and gradually dies.

Conclusion: This activity shows that roots are necessary to keep the plant healthy and alive.

Activity 6

Aim: To see that plant roots hold/anchor the plant in the soil.

Materials Required: Seeds of gram and maize, bowls, cotton wool and water.

Procedure:

  1. Take two bowls and place some wet cotton in them.
  2. Put 3-4 seeds of gram in one bowl and maize in the other.
  3. Keep the cotton wet by sprinkling water every day, until the sprouts have grown into young plants.
  4. After a week, try to separate the young plants from the cotton.

Observation: We will find that it is difficult to pull the plant out as roots established anchor the plant firmly. Conclusion This activity shows that plant roots help in holding the plant firmly in the soil.

Activity 7

Aim: To observe the structure of an ovary in a flower.

Materials Required: Flowers of China rose, a blade, water, a magnifying glass, and a sheet of paper.

Procedure

  1. Take 2 flowers of China rose.
  2. Remove sepals and petals.
  3. With the help of a blade, carefully cut the ovary of one flower longitudinally and of another flower transversely.
  4. Put a drop of water on the cut pieces of ovary to Prevent drying
  5. Observe the structures with a magnifying glass

CBSE Notes Class 6 Science Getting To Know Plants The Structure Of A Ovary In A Flower

Observation: We will observe small bead-like structures inside the ovary.

Conclusion: Small bead-like structures inside the ovary are called ovules.

CBSE Notes For Class 6 Science Chapter 3 Separation Of Substances

Separation Of Substances

Those materials that contain one or more than one type of constituent particles or components are called substances. These occur in nature both in pure and impure or mixed forms.

CBSE Notes For Class 6 Science Chapter 3 Separation Of Substances

Pure Substances

These are substances that are made up of only one kind of particle, for example, silver, gold, iron, etc. They cannot be separated into two or more substances.

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Mixtures or Impure Substances

These are the substances made up of two or more pure substances, for example, air is a mixture of many gases like nitrogen, oxygen, and carbon dioxide. The different substances present in a mixture are called its components or constituents.

The constituents of a mixture are segregated from each other by a process called separation. For example, grain is separated from stalks, tea leaves are separated from the liquid with a strainer while preparing tea, milk, or curd is churned to separate the butter.

CBSE Notes For Class 6 Science Chapter 3 Separation Of A Substances

Purposes Of Separation Of Substance

Most substances that occur in nature may contain one or more useful substances or one useful substance and one or more harmful or unwanted (undesirable) substances.

To make the available substance fit for use, these impurities must be separated from the useful substance. The substances to be separated may be particles of different sizes or materials. These may be solids, liquids, or even gases.

The separation of substances is carried out for the following purposes

  1. To remove impurities or harmful components For example, small pieces of stones and undesirable seed grains are removed from rice and dais before cooking. The useless pieces of stones and seed grains are thrown away.
  2. To remove non-useful components, For example, tea leaves are separated from the liquid with a strainer while preparing tea.
  3. To separate two different, but useful components A mixture may contain one or more useful constituents. These should be separated for their proper use. For example, milk or curd is churned to obtain butter and buttermilk.

Methods Of Separation

Separation of useful substances from unwanted substances is very common in our day-to-day lives and laboratories/industries. In day-to-day life, we use simple methods to carry out separation.

Some most commonly used methods for separating the constituents of a mixture are shown below

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Sepration of soild and liquid mixture

Handpicking

The process of separating solid particles from a mixture by hand is called handpicking. This method is used to separate slightly larger-sized particles present in small quantities (impurities) like stone, husk, pieces of dirt, etc. from the grains of wheat, rice, pulses, etc.

Hence, in such cases where the quantity of such impurities is not very large, handpicking is a convenient method of separating substances.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Handpicking Stones From Grains

Threshing

It is the process of separating grains from stalks of harvested crops. Fully matured crops like paddy (rice) or wheat are harvested from the field. During this, the crop plants are cut close to the ground.

Stalks are dried in the Sun before the grains are separated. Each stalk has many grains attached to it. The grains attached to the stalks are covered in a thin layer called chaff.

The grains are then separated from stalks by the process of threshing. In this process, the stalks are beaten to free the grain seeds.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Threshing Of Paddy Stalks

Threshing can be done by following the ways

  1. By holding the bundles of stalks in hand and beating them on hard surfaces.
  2. By allowing bullocks to trample the stalk.
  3. By machines, in case of large quantities of grains.

Winnowing

The method used to separate heavier and lighter components of a mixture by wind or by blowing air is called winnowing.

This method is commonly used by farmers to separate lighter husk particles (thin, dry outer covering of various seeds) from heavier seeds of the grains.

The steps involved in the separation of husk from grains with the help of wind are as follows

  1. The mixture of wheat grains and husk is taken in a winnowing basket (also called chhaaj in Hindi) plate or newspaper.
  2. Farmers take this mixture in open ground and stand on a risen or elevated platform.
  3. The winnowing basket containing the mixture is held at shoulder height then the mixture is allowed to fall by shaking the basket continuously.
  4. As a result, lighter husk particles are carried away by the blowing wind. Heavy wheat grains fall straight to the ground and form a heap near the platform for winnowing.
  5. The separated husk is used for many purposes such as fodder for cattle.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Sepration of husk from wheat grains by winnowing

Sieving

  • The process of separating very fine particles from bigger ones by using a sieve is called sieving. In this method, a sieve having small holes at its bottom is used.
  • The sieves can be of different sizes which depends on the size of the substances to be separated. Sieving is used when components of a mixture have different sizes.
  • Some examples of separation of mixtures by sieving are as follows

Sieving allows the fine flour particles to pass through the sieve holes while the bigger impurities (Bran-outer coarse part of the grain) remain on the sieve

CBSE Notes For Class 6 Science Chapter 3 Separation Of Substances Sieving of flour to separate wheat bran and fine floor

Science Insight Sieving of wheat flour is not considered a healthy practice because wheat bran which is removed during sieving is a rich source of fibre.

  1. On a large scale, such as in a flour mill, impurities like stones and husk are removed from grains before grinding them. Usually, a hag full of wheat grains is poured on a slanting sieve.
  2. The sieve removes pieces of stones, stalks, and husks that may remain with wheat grains after threshing and winnowing Similar slanting sieves are used at construction sites to separate pebbles and stones from coarse sand.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Pebbles and stones are removed from sand by sieving

Sedimentation, Decantation and Filtration

We observed that sometimes, separation of the mixture is not possible with the help of winnowing and handpicking as there may be lighter impurities present such as dust or soil particles. So, we use other methods for the separation of such a mixture. These methods are as follows

Sedimentation

The process of settling down of insoluble heavy solid particles in a mixture at the bottom of the vessel is known as sedimentation. For example, when we mix up sand and water in a glass and stir it with a spoon or any other tool and wait for some time, we see that the sand settles down at the bottom and clear water stands on it.

The solid settled at the bottom of the glass is known as sediment and the clear liquid above is known as supernatant.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Sedimentation

Decantation

The process of transfer or separation of clear liquid from one vessel to another vessel without disturbing the sedimented particles is known as decantation. For example, transfer of water to another vessel from a mixture of water and sand.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Decantation

The same principle is used for separating a mixture of two liquids, that do not mix, example oil and water can be separated from their mixture by this process.

If a mixture of such liquids, which do not mix, is allowed to stand for some time, they form two separate layers. The component that forms the top layer (i.e. oil) can then be separated by decantation.

Filtration

The process of removing insoluble solid particles from a liquid by using a filter is known as filtration. Common examples of filters used are sieve, muslin cloth, and filter paper.

Some examples of separation mixtures by filtration are as follows

  1. Separation of tea leaves from prepared tea by using a strainer.
  2. Fruit and vegetable juices are usually filtered before drinking to separate the seeds and solid particles of pulp.
  3. The method of filtration is also used in the process of preparing cottage cheese (paneer) in our homes. You might have seen that for making paneer, a few drops of lemon juice are added to milk as it boils.
  4. This gives a mixture of solid particles of paneer in a liquid. The paneer is then separated by filtering the mixture through a fine cloth or a strainer. Sometimes water supplied through taps or water that is collected from ponds or rivers may be muddy, especially after rains.
  5. Therefore, we can use sedimentation, decantation, and filtration processes in a sequence to make the water suitable for usage

Science Insight Our kidneys act as a filter to clean the blood. Waste chemicals dissolved in the blood pass through a membrane in the kidneys and are excreted as urine acts or gets filtered.

Evaporation

The process of conversion of water into its vapor is called evaporation. Heat and wind help in the evaporation of water. The process of evaporation takes place continuously, wherever water is present.

This process is used to obtain a solid material that has dissolved in water or any other liquid. The dissolved substance is left as a solid residue when all the liquid gets evaporated. For example, obtaining salt from seawater.

Sea water contains large amounts of salt dissolved in it. One of these salts is the common salt. Now, understand the way by which it can be obtained.

When seawater is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapor through evaporation.

In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from these solid salts by further purification.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Obtaining Salt From Seawater

Condensation

The process of conversion of water vapor into its liquid form is called condensation. The process of condensation is the opposite of evaporation. In this process, water vapor condenses into a liquid after making contact with the cooled surface.

This method is used when the solid and liquid both need to be recovered, for example, the separation of pure water from salt solution.

Use Of More Than One Method Of Separation

We have studied some methods for the separation of substances from their mixtures. Often, only one method is not sufficient to separate the different substances present in a mixture.

In that situation, we need to use more than one of these methods, for example, the mixture containing salt, sand, and water cannot be separated by a single separation method. With the help of activity 3, we can easily understand the process of separation of a mixture with the help of more than one method.

Solution

It is a mixture in which a substance completely dissolves in a liquid. Here, the substance that dissolves in a liquid is called solute (smaller quantity), while the liquid in which solute is dissolved is called solvent (larger quantity). Solute + Solvent = Solution for example, in a salt solution, salt is the solute and water is the solvent.

Science Insight Water is considered the ‘universal solvent1 as it dissolves a large number of substances in it.

Saturated Solution

We have noticed that many substances dissolve in water and form a solution. But when more and more quantity of these substances are added to a fixed quantity of water, at a given temperature substances remain undissolved and settled down, this means that no more substance can be dissolved in the amount of water we have taken. Such a solution is called a saturated solution. In other words, a solution in which no more soluble substance can be dissolved at a given temperature is called a saturated solution.

Activity 1

Aim: To separate clear water from muddy water by using processes like sedimentation, decantation, and filtration.

Materials Required: 2 glasses, muddy water, filter paper/piece of cloth, funnel, etc.

Procedure:

  1. Take half a glass of muddy water. Let it stand for half an hour.
  2. We observe that after some time, soil settles at the bottom. This process is called sedimentation.
  3. Now, slightly tilt the glass without disturbing the sedimented soil. Let the water from the top flow into another glass. This process is called decantation.
  4. The water in the second glass is still muddy or brownish.
  5. To filter this muddy water first fold the filter paper to make a cone then fix this cone onto the funnel. Pour the muddy water through it.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Separating the two components of a mixture by sedimentation and secantation

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Folding A Filter Paper To Make A Cone

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Set Up For Filtration

Observation: Solid particles in the mixture do not pass through the funnel and remain on the filter paper. Conclusion We can conclude that the given muddy water can be turned into clear water by using the processes of sedimentation, decantation, and filtration.

Activity 2

Aim: To separate salt dissolved in water by evaporation.

Materials Required: Salt, water, teaspoon, beaker (150 mL), burner, tripod stand, wire mesh, China dish, etc.

Procedure:

  1. Take a teaspoon of salt and dissolve it in lOOmL of water in a beaker.
  2. Heat the beaker containing salt and water as shown in.
  3. Continue the heating process until the water gets completely vapourised

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Heating A beaker Containing Salt Water Solution

Observation: After the complete vapourization, there is a white residue left behind in the beaker. Now scrap it out in a China dish and taste it. It is a salt.

Conclusion: We conclude that a substance (like salt) which is soluble in a liquid (like water) forming a salt solution, can be separated through the process called evaporation.

Activity 3

Aim: To separate salt and sand present in water.

Materials Required: Sand, salt, beakers, water, glass rod, kettle, metal plate, ice, burner, etc.

Procedure:

  1. Take a mixture of sand and salt. Keep this mixture in a beaker.
  2. Add a small quantity of water to the beaker and stir the solution with the help of a glass rod. After stirring, allow it to stand for some time.
  3. We observe that salt dissolves in water and sand settles at the bottom ofthe beaker.
  4. Separate sand from solution by decantation or filtration.
  5. Now, we need to separate salt from the remaining mixture of salt and water.
  6. Transfer this liquid to a kettle and close its lid. Heat the kettle for some time.
  7. We notice that the steam comes out from the spout of the kettle.
  8. Now, take a metal plate with some ice on it.
  9. Hold the ice plate just above the spout ofthe kettle. We will observe that when the steam comes in contact with the metal plate, it gets cooled down by ice.
  10. The water droplets fall from the plate and get collected in a separate beaker. This process is called condensation.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Evaporation And Condensation

Observation: We have thus, separated sand (in step 4), and collected water in a separate beaker, and at the end of the activity the white residue left in the kettle is salt.

Conclusion: We conclude that processes of decantation, filtration, evaporation, and condensation are used to separate a mixture of salt, sand, and water.

Activity 4

Aim: To prepare a saturated solution of salt in water.

Materials Required: Spoon, tumbler/ glass, water, salt, glass rod, etc.

Procedure:

  1. Take a tumbler/glass and put 150 mL of water in it.
  2. Add one teaspoonful of salt to the water and stir it with a spoon or glass rod until the salt dissolves completely.
  3. Again, add a teaspoonful of salt and stir it well.
  4. Continue adding salt to water with constant stirring to dissolve it.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Dissolving Salt In Water

Observation: After adding many spoons of salt, it is observed that some salt is left undissolved at the bottom of the tumbler even after stirring. The solution is now said to be saturated.

Conclusion: We conclude that when no more amount of solute (salt) can dissolve in the solvent (water), the solution is called a saturated solution.

Activity 5

Aim: To show the effect of heating on the saturated solution of salt and water.

Materials Required: Tumbler/beaker, water, glass rod, salt, burner, tripod stand, wire mesh, etc.

Procedure:

  1. Take some water in a tumbler or beaker.
  2. Add salt with continuous stirring with the help of a glass rod until it becomes a saturated solution.
  3. Now, add a small quantity of salt to this saturated solution and heat it.
  4. Let this hot solution cool down and observe it.

CBSE Notes Class 6 Science Chapter 3 Separation Of Substances Effect Of Heating On Saturated Solution Of Salt And Water

Observation: After heating the saturated solution, it is observed that the undissolved salt at the bottom of the beaker gets dissolved. However, after cooling down the solution, the salt appears to be settled at the bottom of the beaker again.

Conclusion: We conclude that there is an effect of heating (temperature) on the saturated solution and thus, a larger quantity of salt can be dissolved in water on heating.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups

Sorting Materials Into Groups

Anything that can be seen and touched is called an object. We see a large number of objects around us. For example, a chair, a bullock cart, a cycle, cooking utensils, books, clothes, toys, water, stones, vegetables, plants, animals, etc.

All these objects have different shapes, colours and uses. The matter of which an object is made is called material. All objects are made up of one or more materials. For example, the chair and table are made up of wood here, wood is a material.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups

Grouping Of Objects

Objects can be grouped according to the materials they are made up of.

  1. The same object can be made up of different materials, Example plates can be made up of steel, glass, and plastics similarly, toys can be made up of plastics, rubber, metal, etc.
  2. Different objects can be made up of the same material, Example wood, which can be used to make chairs, tables, beds, ploughs, etc. Similarly, leather can be used to make belts, wallets, purses, bags, etc.

We can also separate materials into several groups based on similarities or differences in their properties.

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Properties Of Materials

Different materials have different properties. Material to make an object is chosen depending on its properties and the purpose for which the object is to be used.

For example, we make a tumbler from materials such as glass, plastic or steel because all these materials have the property of storing water or other liquids. We cannot make a tumbler from a piece of cloth because it cannot hold water.

Similarly, it would not be a wise idea to use paper-like materials for cooking vessels. Some of the properties of materials based on which they can be chosen for different purposes are explained below.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Properties Of Materials

Appearance

Some materials may appear shiny, while some might seem dull. For example, gold, silver, aluminium, and iron shine, while wood, plastic, paper, and rubber are dull.

Materials which appear shiny are said to have lustre (or in Hindi chamak). These materials often lose their shine due to the action of air and moisture. Flowevcr, their shine reappears after rubbing or cutting the surface. That’s why lustre is often noticed on freshly cut ends.

Dull materials remain the same even after rubbing or cutting them. Some materials differ in colour, glow and texture of their surfaces as well, (i.e. rough or smooth) and can be grouped accordingly.

Hardness and Softness

  1. Those materials which cannot be compressed or scratched easily are called hard materials. For example, iron, steel, wood, stone, etc.
  2. Those materials which can be easily compressed or scratched are called soft materials. For example, cotton, wool, clay, butter, etc.
  3. Science Insight Diamond is the hardest known material. It cannot be scratched by other materials and only be cut by the diamond itself.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups

Soluble or Insoluble

Solubility is defined as the ability of a solid, liquid or gaseous substance to dissolve in a solvent (usually a liquid). Based on solubility in water, the material can be soluble or insoluble. Those materials which are completely dissolved or disappear in water are called soluble materials.

Those materials which are not dissolved or disappear in water even after stirring for a long time are called insoluble materials.

Water plays an important role in the functioning ofour body because it can dissolve a large number of substances. Solubility of Solids in Water Some solids completely dissolve or disappear in water, for example, salt, sugar, etc.

Some solids do not dissolve or disappear in water, for example, sand, dust, chalk powder, plastic, etc. They settle down or float on water.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Salt Is Soluble In Water And Sand Is Insoluble In Water

Solubility of Liquid in Water

Some liquids get completely mixed or dissolve in water, for example, vinegar, etc. On the other hand, some liquids do not mix with water and form a separate layer when kept aside for some time, for example, mustard oil, coconut oil, etc.

Solubility of Gases in Water

Some gases are soluble in water while others are not. For example, oxygen gas dissolves in water and is very important for the survival of animals and plants that live in water.Carbon dioxide gas also dissolves in water and helps in photosynthesis in underwater plants. Some gases like nitrogen and hydrogen are not dissolved in water.

Objects may Float or Sink in Water

Some materials that are not mixed or dissolved in water either float on the surface of the water or sink to the bottom of the tumbler.

The property of a material to float on the surface of the water is called flotation and these materials are called floating materials, Example dried leaves fall on the surface of a pond. These materials are lighter than water.

The heavy materials that sink easily to the bottom of the tumbler are called sinking materials, for Example stones thrown into the pond, drops of honey in water, etc. These materials are heavier than water.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Some Objects Floats On the Surface Of Water While Others Sink Into it

Science Insight Ships and boats float higher in the salty sea water than they do in the freshwater of lakes and rivers. This is because salt in seawater makes it denser than freshwater.

Transparency

The property of a material which allows the light to pass through it is called transparency. Based on this property, materials can be classified as follows

1. Transparent Materials

The materials through which an object can be seen are called transparent materials, for example, glass, water, some plastics, etc.

2. Translucent Materials

The materials through which an object can be seen, but not clearly, are called translucent materials, for example, oiled paper, muslin cloth, frosted window, etc.

3. Opaque Materials

The materials through which we are not able to see anything are called opaque materials, for example, wood, cardboard, brick, metal, etc.

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Transparency

Importance Of Sorting Materials Into Groups

In everyday life we often group materials for our convenience as grouping of materials helps us to locate them easily.

For example, in the library, books are arranged in alphabetical order. In grocery stores, household items and eatables items are placed separately. The grouping of materials makes it convenient to study their properties.

Activity 1

Aim: To separate the shiny materials from paper, cardboard wood, copper wire, aluminium sheet, and chalk.

Materials Required: Paper, cardboard, wood, copper wire, aluminium sheet, chalk.

Procedure:

  1. Collect some small pieces of given materials.
  2. Observe the shine in all materials.
  3. You can rub the surface of materials or cut to see if it
    has lustre or not.
  4. Separate the shiny materials.
  5. Note your observations in the table given below.

Sorting Materials Into Groups Activity 1 Given materials Shiny materials

Observation:

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Activity 1 Given materials Shiny materials.

Conclusion: Some of the given materials like copper wire aluminium sheets, have a shiny appearance while others have a dull appearance. The materials with shiny appearance are said to have lustre.

Activity 2

Aim: To observe whether different solid materials (like sugar, salt, chalk powder, sand, and sawdust) are soluble or insoluble in water.

Materials Required: Beakers, spoon, water and solid materials like sugar, salt, chalk powder, sand, and sawdust.

Procedure:

  1. Collect samples of some solid materials.
  2. Take five beakers. Fill each of them up to two-thirds volume with water.
  3. Add a small amount of each given material, in different beakers separately.
  4. Stir the contents of each beaker with the help of a spoon.
  5. Note your observations in the table given below

Sorting Materials Into Groups Activity 2 Solid Materials Disappers In Water Does not Disapper In Water

Observation

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Activity 2 Solid Materials Disappers In Water Does not Disapper In Water.

Conclusion: You will notice that some solid materials have completely disappeared and thus, are soluble in water. Whereas other solid materials like sand, chalk powder, and sawdust do not disappear and are thus, insoluble in water.

Activity 3

Aim: To observe whether liquid samples, like lemon juice, vinegar, mustard oil, coconut oil, and kerosene are soluble or insoluble in water.

Materials Required: Glass tumbler, water, a sample of vinegar, lemon juice, mustard oil, coconut oil, and kerosene.

Procedure:

  1. Collect given samples of liquids like lemon juice, vinegar, etc.
  2. Take a glass tumbler. Fill it half with water.
  3. Add a spoonful of one liquid to this and stir it well,
  4. Let it stand for five minutes.
  5. Observe whether the liquid mixes with water.
  6. Repeat the same procedure with other given liquids also.
  7. Write observations in the table given below.

Sorting Materials Into Groups Liquid Mixes Well Does Not Mix in water

Observation:

CBSE Notes For Class 6 Science Chapter 2 Sorting Materials Into Groups Liquid Mixes Well Does Not Mix in water.

Conclusion: We notice that some liquids like vinegar, and lemon juice get completely mixed with water.

So, these are soluble in water while liquids like mustard oil, coconut oil, and kerosene do not get mixed with water and form a separate layer when kept for some time. So, these are insoluble in water.

Activity 4

Aim: To differentiate between translucent and opaque materials.

Materials Required: Electric bulb, sheet of paper, oil, torch.

Procedure:

  1. Take a sheet of paper.
  2. Look through it towards a lighted bulb.
  3. Make a note of your observations.
  4. Now, put 2-3 drops of some oil and spread it on a sheet of paper.
  5. Look again towards the lighted bulb through it.
  6. Note your observations again.
  7. Now, take a torch and cover the glass of the torch with your palm in a dark place.
  8. Switch on the torch and observe the other side of your palm.

Observation:

  1. When we look at the lighted bulb through the paper, we do not see any light.
  2. When we spread some oil on the paper and look at the lighted bulb through it, we see some light, but not as clearly.
  3. When we cover the glass of the torch with our palm and switch on the torch, we see a small amount of light on the other side of the palm.

Conclusion: We find that materials, in which an object can be seen, but not clearly are called translucent.

Materials which does not allow any light to pass through are called opaque. Hence, in the above observation, paper is an opaque material while paper spread with oil and palm is translucent.

CBSE Notes For Class 6 Science Chapter 1 Components Of Food

Components Of Food

Each food item is usually made up of one or more ingredients, which we get from plants or animals. These ingredients contain some components, which are needed by our body. These components are known as nutrients.

Thus, nutrients are the substances which are required by our body to grow, function properly and stay healthy.

CBSE Notes For Class 6 Science Chapter 1 Components Of Food

The food items based on the presence of these nutrients can be classified as

  1. Energy-giving foods These food items are mainly rich in carbohydrates and fats.
  2. Body-building foods These food items are rich in proteins.
  3. Protective foods These food items are rich in vitamins and minerals.

Apart from these, our body requires water and roughage to function properly

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Science Insight Our nails, hair and skin are made up of keratin protein. The human brain is composed of about 60% fats and it relies on dietary fats for optimal function.

Vitamins

Some vitamins, their sources and their functions are tabulated below.

CBSE Notes For Class 6 Science Chapter 1 Vitamins

Minerals

CBSE Notes For Class 6 Science Chapter 1 Minerals

Science Insight Zinc is an essential mineral for our sense of taste and smell. Its deficiency can create problems with the ability to taste and smell food.

Water

Water performs the following functions

  • It helps our body to absorb nutrients from food.
  • It helps in throwing out waste materials from the body as urine and sweat.

Lack of water in the body causes dehydration. Severe dehydration can even cause death.

Roughage (Dietary Fibre)

It is the fibrous matter present in food that cannot be digested. Roughage is mainly comprised of an indigestible carbohydrate called cellulose, which is present in plants.

Balanced Diet

The total amount of food that a person eats during the entire day is called their diet. A balanced diet is a diet that contains the proper amount of all the nutrients along with a good amount of roughage and water.

It provides the body with all the energy and fulfils various nutrient requirements needed for proper functioning. A balanced diet should include foods that are

  1. Energy-rich Fats and carbohydrates like butter, rice and chapatis.
  2. Body-building Proteins like pulses, peas and fish.
  3. Protective Vitamins, and minerals containing curd, vegetables and fruits.

CBSE Notes For Class 6 Science Chapter 1 A balanced Diet

A balanced diet is not the same for everyone. It depends on age, sex and the type of work that one does. This can be explained by the following examples

  1. In early childhood, the child grows rapidly. So, he or she needs more proteins.
  2. Nursing mothers and pregnant women also need more protein to serve the needs of the growing baby.
  3. A hard worker, i.e. labourer needs more energy, which he can get by eating more fats and carbohydrates

Loss of Nutrients in Food

Eating the right kind of food is not enough. It should also be cooked properly so that its nutrients are not lost. We all know that cooking improves the taste of food and makes it easier to digest. At the same time, cooking also results in the loss of certain nutrients.

So, while cooking we should remember the following important things

  • The skins of many vegetables and fruits contain vitamins and minerals.
  • If the vegetables and fruits are washed after cutting or peeling them, it may result in the loss of some vitamins.
  • Repeated washing of rice and pulses may result in the loss of some vitamins and minerals present in them.
  • Many useful proteins and minerals are lost if excess water is used during cooking and is later thrown away.
  • Vitamin C gets easily destroyed by heat during cooking.

CBSE Notes For Class 6 Science Chapter 1 Components Of Food

Deficiency Diseases

The diseases which occur due to the lack of specific nutrients in our diet over a long period are called deficiency diseases. When a person eats food that does not contain a particular nutrient over a long period, then the person may suffer from its deficiency.

  • A deficiency of one or more nutrients can cause diseases or disorders in our body.
  • Due to the deficiency of one or more nutrients, a person shows the following symptoms
  • Deficiency of protein in a person may cause stunted growth, swelling of the face, discolouration of hair, skin disease and diarrhoea.
  • Deficiency of both proteins and carbohydrates affects a person’s growth and it may stop completely. Such a person becomes so lean and weak that he/she may not even be able to walk.
  • A deficiency of vitamins and minerals may also result in certain diseases,

Some Diseases are caused by the deficiency of vitamins 

CBSE Notes For Class 6 Science Chapter 1 Some Diseases Caused By The Deficiency Of Vitamins

CBSE Notes For Class 6 Science Chapter 1 Some Diseases Caused By The Deficiency Of Minerals

All deficiency diseases may be prevented by taking a balanced diet

Food is said to be fortified when essential vitamins and minerals are added to common foods like rice, wheat, oil, milk and salt to increase their nutritional value. Given alongside is the logo for fortified foods as per standards by FSSAI.

Science Glossary

  1. Balanced diet A diet that contains an adequate amount of all nutrients, for healthy functioning of the body.
  2. Beriberi Disease is caused by a deficiency of vitamin B1. Carbohydrates provide energy to our body. It includes starch and sugar. Energy It is the capacity to do work.
  3. Fats These are the storehouse of energy in our body. Nutrients The fundamental components of food, that provide nourishment to the body.
  4. Proteins These are body-building foods that help in repairing and maintaining the body tissues.
  5. Roughage These are dietary fibre, which forms bulk and helps in the removal of undigested food. Starch is a complex carbohydrate.
  6. Scurvy Disease is caused by a deficiency of vitamin C. Vitamins and minerals These are protective food that helps our body to fight against diseases.

Activity 1

The presence of carbohydrates in the food

Aim: To test the presence of starch in a food item, for Example potato.

Materials Required: Potato, knife, tincture iodine, water, test tube, dropper and plate.

Procedure:

  1. Firstly, we will prepare an iodine solution by adding a few drops of tincture iodine to a test tube half-filled with water. Then mix it thoroughly.
  2. Now, cut a slice of potato with the help of a knife and place it on a plate.
  3. Add 2 to 3 drops of dilute iodine lypS solution to the potato sample. Testing of starch

Observation: We will observe that the colour of the potato slice changes to a blue-black colour.

Components Of Food Testing Of Starch

Conclusion: The appearance of a blue-black colour confirms the presence of starch in the given food sample, i.e. potato.

Activity 2

We can test the presence of protein in food

Aim: To test the presence of proteins in a food material, Example paneer.

Materials Required: Paneer, copper sulphate, test tube, water, caustic soda, dropper, test tube stand, mortar and pestle.

Procedure:

  1. Prepare the copper sulphate solution by dissolving
  2. 2 gram of copper sulphate in 100 mL of water.
  3. Dissolve 10 grams of caustic soda in 100 mL of water to prepare caustic soda solution.
  4. Now grind the food material, i.e. paneer into a thin paste, with the help of mortar and pestle. Transfer the paste to a clean test tube.
  5. Add 10 drops of water to this test tube and shake it well.
  6. Now, using a dropper add two drops of freshly prepared copper sulphate solution.
  7. Then add ten drops of caustic soda solution to the test tube and shake it well.
  8. Place the test tube on the test tube stand for a few minutes.

Observation: After a few minutes, we will observe that the content of the test tube turns violet.

Conclusion: The change of colour in the test tube to violet signifies the presence of protein in the given food material, i.e. paneer.

Activity 3

The presence of fat in the food can be identified by a simple test 

Aim: To test the presence of fat in food material, for example, butter.

Materials Required: Butter, brown paper a source of light (bulb), knife.

Procedure:

  1. Cut a small quantity of food material.
  2. Put the food material on brown paper and rub over it.
  3. Now, hold this brown paper towards a source oflight. Observation Under the light will observe a bright, greasy patch on the paper.

Conclusion: The greasy patch confirms the presence of oil, i.e. fat in the food item.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms: Characteristics And Habitats

The Living Organisms: Characteristics And Habitats

Living organisms can be found everywhere on the Earth including extremely hot deserts, cold mountains, deep oceans, and even in the openings of volcanoes. All these places are so different from each other, yet all of them have living organisms of various kinds.

In the mountains of the Himalayas, where it is very cold, many kinds of trees like oaks, pines, and deodars are found.

Similarly, hot desert areas, like Rajasthan, have different kinds of cactus plants and seashore areas like Puri have an abundance of Casuarina trees. Like plants, different kinds of animals are also found in different areas.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Characteristics And Habitats

Organisms And The Surroundings Where They Live

The kinds of plants and animals found in one region are very different from the plants and animals of the other regions. Some of the examples are listed below.

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CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Characteristics And Habitats

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Characteristics And Habitats

Adaptation

Adaptation is the presence of specific features or certain habits that enable a plant or an animal to live in its surroundings naturally. Different animals are adapted to their surroundings in various ways.

For example, the sea and the desert are very different surroundings, and different kinds of plants and animals are found in these two regions. Let us take examples of caramel (from the desert) and fish (from the sea) to understand it better.

1. Adaptations in Camel

The features of a camel, that help it survive in desert conditions are listed below

  1. Camels have long legs which help to keep their bodies away from the heat of the sand.
  2. They excrete a small amount of urine and their dung is dry. They do not sweat. Since they lose very little water from their bodies, camels can live for many days without water.
  3. Padded feet help camel to walk on hot and slippery sand without sinking.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms A camel

2. Adaptations in Fish

The features of a fish which enable it to live in freshwater sea are listed below

  1. They have streamlined shapes. This shape helps them to move inside water.
  2. They have slippery scales on their bodies. These scales protect the fish and also help in easy movement through water.
  3. They have flat fins and tails that help them to change directions and keep their body balanced in water.
  4. Gills present in the fish help them to use oxygen dissolved in water.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Adaptations In fish

Acclimatization

It can be defined as the process where an organism adjusts its behavior or physiology in response to changes in its environment (i.e. altitude, temperature, etc.).

For instance, if we live in the plains and suddenly go to high mountain regions we may experience difficulty in breathing, nausea, headache, etc. This happens because the air supply is reduced at high altitudes.

However, after a few days, our body adapts to this change. This is called the acclimatization of the body to the environment. These changes are different from adaptations that take place over thousands of years.

Habitat

The place where an organism lives, grows, and interacts with other organisms is called habitat. It provides the living organism with food, shelter and favorable climatic conditions to survive, breed, and flourish.

Several kinds of plants and animals may share the same habitat. Living beings live on land, in water, or on trees.

Types of Habitat

Habitat is broadly divided into two types, i.e. terrestrial and aquatic.

  1. Terrestrial Habitats The plants and animals that live on land are said to live in terrestrial habitats, for Example forests, grasslands, deserts, and coastal and mountain regions.
  2. Aquatic Habitats The habitats of plants and animals that live in water are called aquatic habitats, for Example ponds, swamps, lakes, rivers, and oceans.

There are large variations among terrestrial habitats like forests, grasslands, deserts, and coastal and mountain regions located in different parts ofthe world. Similar variations are observed for all aquatic habitats.

Components of a Habitat

  • Habitat consists of living organisms interacting with the environment. It has two basic components.
  • Abiotic Components These include non-living components, for example. air, water, soil, sunlight, rocks, etc.
  • Biotic Components These include living organisms, Exampele plants and animals.

Components of a Habitat

Habitat consists of living organisms interacting with the environment. It has two basic components.

  1. Abiotic Components These include non-living components, for example, air, water, soil, sunlight, rocks, etc.
  2. Biotic Components These include living organisms, for Example plants and animals.

Some Terrestrial Habitats

The organisms that live on land are said to live in terrestrial habitats. Some of them are as follows

Deserts

These habitats include vast areas of land with sand and little or no vegetation. They also get very little rain. These are hot and dry places. Organisms that live here have to cope with these adverse climatic conditions, so they develop adaptations accordingly.

Adaptations in Plants

The desert plants have the following adaptations that help them to survive in hot and dry conditions.

  1. Leaves are either absent or are very small and spiny to reduce water loss through transpiration.
  2. The leaf-like structure in a cactus is its stem. Photosynthesis in these plants is usually carried out by the stem. The stem is also covered with a thick waxy layer which helps to retain water.
  3. Also, plant roots are very deep for absorbing water from larger areas, for example, Acacia, ber, etc.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Some Typical plants that grow in desert

Adaptations in Animals

The desert animals have the following adaptations that help them to survive in hot and dry conditions.

  1. There are desert animals like rats and snakes, which stay in burrows deep in the sand during the daytime to stay away from the intense heat.
  2. These animals come out only during the night when it is cooler.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Desert Animals In Burrow

Science Insight Some animals show behavioral adaptation, A Cape ground squirrel uses a long bushy tail as a parasol or an umbrella. It provides shade in the scorching heat of the Sun.

Mountain Regions

These areas are generally very cold and windy. Some mountains may receive snowfall during winter. As we go up in the mountainous regions, the surroundings change and we see different kinds of adaptations at different heights.

The plants and animals inhabiting these regi show special kinds of adaptations as given below

Adaptations in Plants

There are following features present in plants that help them to survive in mountain regions are

  1. The trees are usually cone-shaped with tilted branches which helps rainwater and snow to slide off easily.
  2. They have thick bark to protect them against the severe cold.
  3. These plants bear needle-shaped leaves, thus reducing water loss.

Adaptations in Animals

The animals living in the mountain regions have the following adaptations

  1. The yak has thick skin or fur to protect them from cold.
  2. The snow leopard has thick on its body including toes and feet This protects its feet from the cold when it walks on the snow.
  3. The mountain goat has long hair to keep it warm and strong hooves for running up the rocky slopes of the mountains.

Science Insight Animals like hedgehogs and dormouse hibernate (deep sleep) throughout the winter to save energy and survive the winter without eating much. They utilize the stored food (as fat) in their bodies.

Grasslands

  1. These habitats include short and tall grasses scattered with small and large trees. Such habitats have hot summers and chilly winters.
  2. Lions and deer have different types of adaptations to survive in the same habitat.

Lion

It is a strong animal that can hunt and kill animals like deer. The adaptations which enable lions to survive in a forest or a grassland are as follows.

  1. It is a light brown which helps it to hide in dry grasslands when it hunts for prey (animals to eat).
  2. It has long claws in its front legs that can be withdrawn inside the toes.
  3. The eyes in front of the face allow it to have a correct idea about the location of its prey

Deer

It is another animal that lives in forests and grasslands. The following features help it to survive in this habitat.

  1. It has strong teeth for chewing hard plant stems in the forest.
  2. A deer needs to know about the presence of predators (animals that feed on other animals, like lions) to run away from them and not become their prey so, it has long ears to hear the movements of predators.
  3. The eyes on the sides of its head allow it to look in all directions for danger.
  4. The speed of the deer helps it to run away from the predators.

Some Aquatic Habitats

The organisms that live in water are said to live in aquatic habitats. These are further subdivided into marine and freshwater habitats.

Oceans

Oceans and seas are marine water habitats. The animals living in the ocean show a variety of shapes and structures. Some examples are given below.

  1. Many sea animals have streamlined bodies to help them move easily in water, Example fishes.
  2. Octopuses and squids do not have this type of body. They stay in the deeper layer of the ocean, near the seabed, and catch any prey that moves towards them. However, while moving in water, they can streamline their bodies.
  3. These animals have gills to breathe and use the oxygen dissolved in water.
  4. Whales and dolphins do not have gills. They breathe in air through nostrils or blowholes. These are located at the upper part of their heads.
  5. This allows them to breathe In air when they swim to the surface of the water. They can stay inside the water for a long time without breathing. They come out to the surface from time to time, to breathe in air.

Ponds and Lakes

  1. The ponds, lakes, and rivers are freshwater aquatic habitats.
  2. The plants which grow in water are called aquatic plants.
  3. All aquatic plants have the following aquatic adaptations
  4. Their roots are either small or not very well developed with the primary function of anchorage.
  5. Their leaves are ribbon-like and long to cope with the water currents.
  6. Stems of these plants are long, hollow, and light with spaces filled with air to keep them floating.
  7. The plant body is covered with mucilage which prevents decay in the water.

There are three types of aquatic plant

  1. Free-Floating These aquatic plants float on water. Their roots are very small and they freely float on the surface of the water, for example, water hyacinths.
  2. Partly Submerged These aquatic plants are fixed in the soil at the bottom by their roots. The stem of these plants grows up to the surface of the waterbody, and leaves and flowers float on the surface of the water, for example, lily and lotus.
  3. Completely Submerged All the parts of such plants like stems, branches, and leaves are underwater. These plants are also fixed to the soil at the bottom by their roots example hydrilla.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Types Of Aquatic Plants

Adaptations In Frog

They usually have ponds as their habitat. Frogs can stay both inside the pond water as well as move on land. They have strong back legs that help them in leaping and catching their prey. They have webbed feet which help them swim in water.

Characteristics Of Living Organisms

A large variety of materials or things are present around us. Some of them are living while others are non-living. Living organisms can be identified based on the following features.

  1. They need food, water, and air to survive.
  2. They can grow.
  3. They can move on their own.
  4. They respond to stimuli.
  5. They reproduce themselves.
  6. They respire and release energy from food.
  7. They excrete and get rid of waste materials from their body.
  8. They have a definite lifespan.
  9. They are made up of living cells.
  10. Non-living things do not perform any of the above functions.

Let us discuss a few important characteristics of living beings in detail

1. Food

  • AH living beings including plants and animals need food to stay alive. Food gives organisms the energy needed to grow. Organisms also need this energy for the life processes that go on inside them.
  • Along with food they also need air and water. Plants make their food with the help of sunlight, air, and water, through the process known as photosynthesis. Whereas animals and humans depend on plants other animals and their products for their survival.

2. Growth

All living things (plants and animals) show growth by increase in size and weight. When living things grow, they become taller and bigger on their own. For example,

  1. A baby grows into an adult.
  2. A small puppy grows and becomes a dog.
  3. A chicken hatched from an egg grows and becomes a hen or a cock.
  4. Similarly, a small plant grows and becomes a big tree.

3. Respiration

  1. It is a vital process carried out by all living organisms. It is through respiration that the body finally obtains energy from the food it takes.
  2. When we inhale, the air moves from the outside to the inside of the body. When we breathe out we expel the air which is inhaled.
  3. Breathing is a part of respiration. All living organisms breathe in oxygen, which is used by the living body and gives out carbon dioxide produced in the process. The mechanism for the exchange of gases is different in different organisms.

Some examples are given below

  1. Earthworm breathes through its skin.
  2. Fishes use gills to obtain dissolved oxygen from water.
  3. Insects have tiny pores on their exoskeleton (body wall).
  4. Plants also respire through tiny pores present on their leaves called stomata.

In sunlight, plants use carbon dioxide in the air to produce their food and give out oxygen. Plants produce their food only during the daytime, whereas respiration in them takes place day and night.

The amount of oxygen released in the process of food preparation by plants is much more than the oxygen they use in respiration.

4. Response to Stimuli

All living things respond to changes around them. The changes in our surroundings that make us respond to them are called stimuli. A few examples are given below

  1. Wild animals run away when a bright light is flashed on them.
  2. Cockroaches begin to move to their hiding places if the light in the kitchen is switched on at night.
  3. We close our eyes when a sudden bright light is flashed or when we suddenly move from a dark place to bright sunlight.
  4. In some plants like Mimosa, commonly known as ‘touch-me-not’ leaves close or fold when someone touches them. Flowers of some plants bloom only at night whereas in some plants flowers close after sunset.

5. Excretion

The process of removal of waste from the body is called excretion.

All living things take food, but not all food that is eaten is used. A part of it that is not used is removed as a waste.

Our body also produces waste products in life processes like respiration, digestion, etc. These waste products are harmful to our body which is why these products have to be removed from our body. Thus, it becomes a necessary process carried out by all living organisms.

Plants also Excrete

The mechanisms of excretion in plants are a little different. Some harmful or poisonous materials are produced in plants as waste.

Some plants find it possible to store the waste products within their parts in a way that they do not harm the plant as a whole.

They shift waste products towards the outermost layer of the stem, making it harder and stronger. Some plants remove waste products as secretions, For Example, gum and resins are excretory products of the plant.

Science Insight The excretory products of plants are used in many ways. For example, resins are used to make paints and varnishes, gums are used to treat wounds, and serve as an important ingredient in adhesives

6. Reproduction

It is the process by which living things produce more of their kind. This is true for both animals and plants.

Reproduction takes place in many different ways in different organisms. Some modes of reproduction are given below

  1. Animals like insects, fishes, and birds lay eggs and when these eggs hatch, the young ones come out and grow into adults,
  2. Some animals like cats, dogs, cows, and human beings give birth to young ones.
  3. Plants also reproduce. Many plants produce seeds which can germinate and grow into new plants.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Birds Lay Eggs Which After Hatching Produces

Some plants reproduce through parts other than seeds, Example a part of a potato with a bud, grows into a new plant. They also reproduce through cutting.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms A Seed From A Plant Germinates Into A Plants

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms A New Plant Grows From A Bud Of Potato

7. Movement

It is one of the most important signs of life in an organism. All living things move by themselves. Animals can from one place to another.

Plants are generally anchored in soil so they do not move from one place to another. However, various substances like water, minerals, and the food synthesized by them move from one part of the plant to another. Also, opening and closing off lower is a movement.

Death

It is another common characteristic of living beings simple. It marks the ending oflife and reproduction is the starting oflife. Reproduction ensures the continuity of particular organisms.

A particular type of organism can survive over thousands of years only if it reproduces its kind. One single organism may die without ever reproducing, but that type of organism can exist only if there is reproduction.

Some Exceptions of Living Organisms

We can conclude that living things may have all the characteristics that we have discussed, while non-living things may not show all these characteristics at the same time.

  • Non-living things like cars, bicycles, clocks, and water in the river move. The Moon moves in the sky, and a cloud grows in size.
  • Sometimes living things may also not show all the characteristics of the living. For example, seeds stay in a shop for months and do not show any growth or some of the other characteristics of life. However, we bring the same seed and plant it in soil, water it and it turns into a whole plant.

Activity 1

Aim: To show the effect of abiotic factors on the germination of seeds to form young plants.

Materials Required: Dry moorig seeds, water, 5-6 containers, refrigerator.

Procedure:

  1. Collect some dry moong seeds.
  2. Keep 20-30 seeds aside and soak the rest in water for a day.
  3. Divide the soaked seeds into four parts, i.e. (Parts A to D).
    1. Part A = Completely submerged in water for 3-4 days.
    2. Part B = In a sunny room
    3. Part C = In a cupboard that does not allow any light to come in.
    4. Part D = In the refrigerator.

4. Let the setup remain undisturbed and observe after a few days.

Observation: After a few days following observations are made

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Observation The Effect Of Abiotic Factors

Conclusion: We conclude that sunlight, air, water, and proper temperature are necessary for the germination of seeds.

Activity 2

Aim: To show that a desert plant loses very little water through transpiration.

Materials Required: One potted leafy plant, one potted cactus plant, two transparent polythene bags, thread.

Procedure:

  1. Take two potted plants, one leafy and another cactus.
  2. Tie separate polybags to both plants and keep them in sunlight.
  3. After a few hours observe the inner surface of polybags.

Observation: We will observe that there are more water droplets in the leafy plant as compared to the cactus plant.

Conclusion: The rate of transpiration (loss of water through leaves) in cactus, is much lower as compared to the leafy plant. This is because of the adaptation acquired by cacti to survive in hot and dry places.

Activity 3 

Aim: To show that sunlight acts as a stimulus for plants.

Materials Required: A potted plant, water,

Procedure:

  1. Place a potted plant in a dark room near a window through which sunlight enters the room as shown in the figure.
  2. Water the plant regularly and observe it for a few days. Observation We will observe that the growth of the plant occurs towards the window from where the plant gets sunlight.

Conclusion: Plants tend to grow toward sunlight so, that they can avail it and carry out photosynthesis. Thus, sunlight serves as a stimulus for plants.

CBSE Notes For Class 6 Science Chapter 6 The Living Organisms Plant Respond To light