Class 8 Science

CBSE Class 8 Science Chapter 13 Light Multiple Choice Questions

Question 1. We can see a non-luminous object when light

1. Emitted by the object falls on the eye
2. Is reflected from the object towards our eye
3. Completely passes through the object
4. Gets completely absorbed by the object

Answer: 2. Is reflected from the object towards our eye

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Question 2. Angle of incidence is equal to the angle of reflection.

1. Always
2. Sometimes
3. Under special conditions
4. Never

Answer: 1. Always

Question 3. Image formed by a plane mirror is

1. Virtual, behind the mirror and enlarged
2. Virtual, behind the mirror and of the same size as the object
3. Real at the surface of the mirror and enlarged
4. Real, behind the mirror and of the same size as the object

Answer: 2. Virtual, behind the mirror and of the same size as the object

Question 4. Which of these objects reflects light?

1. The sun
2. The moon
3. A glowing bulb
4. Burning wood

Answer: 2. The moon

Question 5. A tiny mirror Mis fixed on a piece of cardboard placed on a table. The cardboard is illuminated by light from a bulb. The position of eye with respect to position of bulb is shown in figure as A, B, C and D. In which position, mirror will be visible?

1. A
2. C
3. B
4. D

Answer: 1. A

Question 6. Two mirrors A and B are placed at right angles to each other as shown In figure.

A ray of light incident on mirror A at an angle of 20° falls on mirror Bafter reflection. The angle of reflection for the ray reflected from mirror B would be

1. 25°
2. 70°
3. 50°
4. 115°

Answer: 2. 70°

Question 7. A small hole P Is made In a piece of cardboard. The hole Is Illuminated by a torch as shown in figure. The pencil of light coming out of the hole falls on a mirror

At which point should the eye be placed so that the hole can be seen?

1. A
2. B
3. C
4. D

Answer: 1. A

Question 8. Light is falling on surfaces Si, % S3 as shown in figure.

Surfaces on which the angle of incidence is equal to the angle of reflection is/are

1. Only S1
2. S1 and S2
3. S2 and S3
4. All the three surfaces

Answer: 4. All the three surfaces

Question 9. As the angle between two plane mirrors is decreasing gradually, the number of Images of an object placed between them

1. First increases then decreases
2. First decreases then increases
3. Increases
4. Decreases

Answer: 3. Increases

Question 10. How does the eye change To focus on near or distant objects?

1. The eye lens moves in or out
2. The retina moves in or out
3. The eye lens becomes thicker or thinner
4. The pupil becomes larger or smaller

Answer: 3. The eye lens becomes thicker or thinner

CBSE Class 8 Science Chapter 13 Long Answer Type Questions

Question 1. Them Is n mistake in each of the following ray diagrams given ns figure (a), (b). and (c). Make the necessary correction (s).

Answer: The correct diagrams are as below

Question 2. A man stands 10 m in front of a large plane mirror, so how far must he walk before he is 5 m away from his image?
Answer: As, per the given information, point 0 is initial position of the man and I is initial position of the image of the man can be show with the help of a figure.

Point O’ is final position of the man and I’ is final position of the image of the man. From the figure.

O’P + PI’ = 5m [0’P = PI’]

0’P + 0’P = 5m

0’P = 25m

Distance walked by the man = OP- O’P
= 10-2.5 = 7.5m

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Question 3. Aditya visited a lake on two days. On the first day, the reflection of the surrounding mountains could be seen clearly in water of the lake. On the second day, he was not able to see the reflection of the mountains clearly. Give one possible reason for this phenomenon and explain your answer clearly.
Answer: The unclear image of the mountains on the second day is probably due to wind blowing across the lake causing it to lose its calmness. When the lake is calm, the surface of the lake is smooth and regular reflection occurs, allowing a clear image of the mountains to be formed. When the wind blows across the lake, the surface of the lake becomes rough and uneven causing a diffused reflection, lienee, the image formed of the mountains will be unclear and blurred.

Question 4. Figure shows tho word REST written In two ways In front of a mirror. Show how the word would appear In the mirror?

Answer: According to reflection properties of plane mirror, it forms same size, laterally inverted images of the object infront of them.

Question 5. Boojho planned an activity to observe an object A through pipes as shown in figure, so that he could see objects which he could not directly see.

1. Mention how many mirrors should he use to see the objects?

Answer: Number of mirrors = 3

2. Indicate the positions of the mirrors in the figure.

Answer: Positions of the mirrors are as shown in figure

3. State what must be the angle w.r.t. the incident  light at which he should place the mirrors?

Answer: Mirrors should be placed at 45° w.r.t. the incident light, so that ray can move forward.

4. Indicate the direction of rays in the figure of (2) Part.

Answer: Direction of rays is shown in figure.

5. If any of the mirrors is removed, will he be able to see the objects?

Answer: He will not be able to see the objects ifany of the mirrors is removed, since he will not get the rays after that removed mirror.

CBSE Class 8 Science Chapter 13 Light Short Answer Type Question

Question 1. Look at figure. Can the Image of the child In It be obtained on a screen?

Answer: The image of the child cannot be obtained on the screen because the image is not real. The images formed by plane mirror are virtual, so these virtual images cannot be seen on die screen.

Question 2. What is the difference between the surfaces of a sheet of sandpaper and a mirror?

Answer: The sandpaper has a rough surface causing light that is reflected on it to be scattered at different angles. The mirror however, allows regular reflection. Sandpaper cannot produce any image, unlike the mirror due to diffused (irregular) reflection.

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Question 3. Explain how do we see various objects?

Answer: Due to reflection, we can see various objects. Since, we know that, all surfaces reflect light So when light falls on them (any objects), it reflects the light. In this way, this reflected light enters our eyes and due to this, we can see the object.

Question 4. Draw figure showing the position of the plane mirror. Also, label the angle of incidence and angle of reflection on it.

Answer:

Question 5. “The laws of reflection only holds true for regular reflection”. Is this statement true or false? Explain your answer.
Answer: False, the laws of reflection holds for both regular and diffused reflection. In a diffused reflection, the reflecting surface being rough anil uneven, the parallel beam of light is reflected in different directions and angles.

Question 6. Explain what happens to light when It gets dispersed?Also, give an example.
Answer: Light is splitted into its constituent colours (7 colours) when it gets dispersed, e.g. rainbow formation is due to the dispersion of white light after passing through water droplets.

Question 7. Which part of the eye gets affected, if someone is suffering from cataract? How is it treated?
Answer: In people suffering from cataract, the eye lens becomes cloudy. Cataract is treated by replacing the convex lens with a new artificial lens.

Question 8. Eyes of the nocturnal birds have large cornea and a large pupil. How does this structure help them?
Answer: The size of the eyes of nocturnal bird is large. Large eyes with a wider pupil, larger lens and increased retinal surface can collect more ambient light which help them to see the objects even at night easily. 

Question 9. “Though the image formation on retina is inverted but still we are able to see the erect objects”. Explain how?
Answer: Yes, it is very true to say because the formation ofimage on the retina is conveyed to brain in the form ofelectrical impulses with the help ofoptical nerves. So, brain is able to perceive an erect image ofobject with the help of electrical impulses.

Question 10. Explain in brief, how do ciliary muscles affect the functioning of eye?
Answer: As we know that, ciliary muscles can contract and relax, because of it, this can change the shape of eye lens which results in change in its focal length. So, eye lens can make image of nearby objects and also far off objects on retina.

Question 11. The picture shows the size of the pupil under two different conditions.

What makes the pupil change size between conditions 1 and 2?

Answer: In condition 1, eyes get insufficient amount oflight. That’s why, the pupil expands but in condition 2, eyes get large amount of light that’s why pupil contract.

Question 13. Boojho stands at A just on the side of a plane mirror as shown In figure. Can he see himself in the mirror ? Also, can he see the image of objects situated at P, Q and R?

Answer: As Boojho is not in the range of reflecting surface rather, he is standing away from the mirror, so he cannot see himself in the mirror. But he can see the image ofP which is in the reflecting area but not ofQ and R.

Question 14.

1. Find out the position of the Image of an object situated at A In the piano mirror.
2. Can Pahell at B see this Imago?
3.  Can Boojho at C see this Image?
4. When Pahell moves from B to C, where does the Image of A move?

Answer:

1. Since, it is plane mirror, so the image is formed behind the mirror and there is a lateral inversion in it

1. Yes, Paheli can see the image of object A.
2. Yes, Boojho can also see the image of object A.
3. No change in the position of the image of A

CBSE Class 8 Science Chapter 13 Light Very Short Answer Questions

Question 1. Why are we able to see the tap water in the glass even though It Is colourless?
Answer: Tap water reflects the light into our eyes. As long as an object reflects light into our eyes, we can see it.

Question 2. Light travels fastest in a vacuum. Why?
Answer: Light travels faster in a vacuum than in any other medium because there is no obstruction to the passage of light in a vacuum.

Read And Learn More CBSE Class 8 Science Very Short Questions And Answers

Question 3. Mention the five English letters that do not show lateral inversion on suffering reflection from a plane mirror.
Answer: The five English letters that do not show the lateral inversion on suffering reflection are A, H, O, T, and U.

Question 4. How many times is ray of light reflected by two plane mirrors placed parallel and facing each other?

Answer:

The ray is reflected infinitely between the two plane mirrors placed parallel to each other.

Question 5. The angle between the incident ray and the reflected ray is 60 0. What is the value of the angle of incidence?

Answer: Since the angle of incidence = the angle of reflection. So, angle of incidence = 30°

Question 6. Imagine that parallel rays are incident on an irregular surface. Are the rays reflected from this surface parallel to each other?
Answer: No, the reflected rays from an irregular surface are in different directions.

Question 7. When a parallel beam of light hits an uneven surface, predict the nature of the reflected beam.

Answer: When light hits an uneven surface, there are many angles of incidence. Hence, the parallel beam of light rays will be reflected off the surface at different angles,

Question 8. State the size of the image formed by a plane mirror.
Answer: The size of the image formed by a plane mirror is the same as that of the object in front of the mirror.

Question 9. Mention the name of the device that is generally used by the designers of wallpapers and fabrics.
Answer: A Kaleidoscope is a device that is generally used by the designers of wallpapers and fabrics.

Question 10. White light is a combination of which colours?
Answer: White light is a combination of seven colours, which are Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

Question 11. A safety vest helps to keep workers working by the roadside safe. This is especially so during the benight. Why?
Answer: The reflectors on the safety vest reflect light into the motorist’s eyes. This helps to alert the motorists to the wearer’s presence on the road.

CBSE Class 8 Science Chapter 10 Sound Very Short Answer Questions

Question 1. Does any part of our body vibrate when we speak? Name the part.
Answer: Yes, while speaking, the part that vibrates is called the vocal cords. It is below the throat and creates vibrations while speaking.

Question 2. Explain how you can describe vocal cords.
Answer: The two ligaments which stretch across the larynx in such a way that it leaves a narrow slit between them for the passage ofair, are known as vocal cords.

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Question 3. Name two musical instruments that produce sound by vibrating strings.
Answer: The Guitar and sitar are two musical instruments that produce sound by vibrating strings.

Question 4. Why do we not hear the sound of an explosion on the surface of the moon?
Answer: There is no atmosphere on the moon, and sound waves need a medium to travel, so we cannot hear sound on the moon.

Question 5. How do whales and dolphins hear sound?
Answer: Through water as a liquid medium, both whales and dolphins hear the sound

Question 6. When we hear a sound, does any part of our body
Answer: It is the eardrum that vibrates and sends vibrations to the inner ear when we hear any sound.

Question 7. A baby recognises her mother by her voice. Name the characteristic of sound involved.
Answer: Pitch is that characteristic of sound by which distinction can be made between two sounds.

Question 8. What is the frequency of a wave with a period of 0.025 s?
Answer: Given, T =0.025 s,

⇒ \(\mathrm{v}=\frac{1}{T}=\frac{1}{0.025}=40 \mathrm{~Hz}\)

Question 9. Different bees produce buzzing sounds of different pitches. Which affects the pitch of the bee’s buzzing sound?
Answer: The faster the bee vibrates its wings, rthe greater the frequency of the sound and the frequency of sound. Hence, the higher the frequency, the more will he the pitch.

Question 10. Our steps do not produce a loud sound if we walk on a carpet floor. Explain with the help of a reason.
Answer: As the amplitude of vibrations of the floor is reduced and the sound ot our steps becomes feeble, so due to this reason, we do not produce a loud sound when we walk on a dry carpet floor.

Question 11. Mention the name given to the maximum displacement of a vibrating body from its central position.
Answer: Amplitude is a name given to the maximum displacement of a vibrating body from its central position.

Question 12. Explain why babies have a feeble sound.
Answer: Due to the small amplitude of their sound, babies have a teething sound

Question 13. Three different vibrating objects produce three types of sounds, X, V, and Z. The sounds X and Y cannot be heard by a man having a normal range of hearing, but sound Z can be heard easily. The sound X can be heard by a bat, whereas sound Y can be heard by a rhinoceros. What type of sounds are X, Y, and Z?
Answer: X is ultrasonic sound, Y is infrasonic sound, and Z is audible sound.

Question 14. Lightning can be seen at the moment when it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (Speed of sound =330 m/s)
Answer: We know that,

• Distance = Speed x Time = 330 x 5 =1650 m
• = 1.65 km (Y 1 km =1000 m)
• So, she is standing 1.65 km from the place where the lightning occurs.

Question 15. A hearing aid that is attached to the ear helps people who suffer from hearing loss. What is the main function of the hearing aid?
Answer: The hearing aid amplifies the sound received from the surroundings.

CBSE Class 8 Science Chapter 13 Light Activities Activity 1

Aim To understand the reflection by a plane mirror.

Material Required Drawing board, white sheet, comb, plane mirror, black paper, and a torch.

Procedure

1. Fix the white sheet of paper on the drawing board.
2. Take the comb and close all its holes except one present in the middle with the help of black paper.
3. Hold the comb perpendicular to the drawing board.
4. Now, take the torch and throw light on the comb. Light must fall on the opening of the comb.
5. 5. You will see a ray of light falling on the drawing board. Place a plane mirror in the path of light and observe what happens to the ray coming from the comb.

Conclusion The light ray strikes with the mirror and changes its path. The ray coming from the comb is incident ray and the ray going after striking the mirror is reflected ray.

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Activity 2

Aim To understand the second law of reflection.

Material Required A chart paper (white) , a plane mirror, a comb, black paper and a torch.

Procedure

1. Spread the white chart paper on the table such that it extends little beyond the edge of the table.
2. Close all the holes of the comb with black paper, except one at the middle.
3. Place plane mirror and comb perpendicular to the table as shown
4. You will see the incident ray and reflected ray on the while chart paper. Now, bend the chart paper at the end of the table.
5. You will not see the reflected ray on the bended portion of the chart paper. Now, bring the paper back to its original position. You will again see the reflected ray.

Conclusion We have concluded that the incident ray, reflected ray and the normal all lie in the same plane.

Activity 3

Aim To study the formation of image by a plane mirror.

Material Required Drawing board, a white paper, a plane mirror, a pencil and a ruler.

Procedure

1. Paste the white paper on the drawing board.
2. Consider that an object is at O. Now, draw two rays OM and OH incident on the mirror.
3. Draw two reflected rays MN and HG by making angle of reflection equal to angle of incidence. Extend these reflected rays further. You will find that they do not meet.
4. Now, extend the two reflected rays using a pencil and ruler behind the mirror (dotted lines). Mark the point 1 where they meet.
5. Since, the reflected rays do not actually meet at 1, we say that it is a virtual image.
6. Measure the distance of object (PO) and distance of image (PI) from the mirror (PQ).

Conclusion

1. The distance of object from the mirror is same as the distance ofthe image from the mirror i.e. PO = PI.
2. The image formed by plane mirror is virtual.

Activity 4

Aim To study the properties of reflection from an irregular surface using laws of reflection.

Material Required White sheet, ruler, protractor and a pencil.

Procedure

1. Drawa rough surface on the white sheet as shown in figure (a).

1. Draw parallel rays which fall on this surface. These rays arc incident rays.
2. Draw perpendicular line at every point of incident on the surface.
3. Now, measure the angle between normal and incident ray for every ray. This is angle of incidence.
4. Draw angle of reflection which is equal to the angle of incidence as shown in figure (b), then draw reflected rays.

Conclusion Incident rays are parallel but reflected rays are not parallel. Hence, irregular surfaces produce irregular or diffused reflection.

Activity 5

Aim To study the number of images formed by two mirrors inclined at some angle.

Material Required Two mirrors, any small object like pen, pencil or rubber.

Procedure

• Place two mirrors at right angles to each other with their edges touching.
• Place the object in between the mirrors. We can see two images in the mirrors.

• Now, change the angle between mirrors (like 45°,60°,120°,180°). You can set angles with the help of a protractor.
• Note down the number of images formed in each case.

Conclusion

1. When angle between mirrors is greater than 90°, then two Images are formed.
2. When the angle between mirrors is less than 90“, then number of images increases.

Activity 6

Aim To build a kaleidoscope.

Material Required Three rectangular mirror stripes (15 cmx 4 cm), circular cardboard tube, cardboard disc, a circular transparent glass plate, a circular grounded glass plate and several small pieces ofcoloured glass or bangles.

Procedure

1. Take the three rectangular mirror strips and join them to form a hollow prism with their reflecting surface facing each other.
2. Fix this prism in a circular cardboard tube and close one end of the tube by a cardboard disc. Make a small hole in this disc.
3. Close the other end of prism with the circular glass plate.
4. Put several pieces of coloured bangles on this plate.
5. Close the end oftube with the grounded circular glass plate. Now, your kaleidoscope is ready.
6. Now, see through the hole and rotate the cardboard

Conclusion We observed different patterns in the kaleidoscope every time. These patterns are visible due to multiple reflection by glass strips.

Activity 7

Aim To show that sunlight is made up of seven colours.

Material Required A howl filled with water, a plane strip of mirror, white paper.

Procedure

1. Place the howl filled with water on a table. Now, place a strip of mirror partially immersed into the water.
2. Place this arrangement near a window such that direct sunlight falls on the mirror.
3. Adjust the mirror in such a way that the reflected light fall on a wall.
4. Place the white paper where the reflected light fall on the wall.
5. Observe the colours of reflected light.

Conclusion Sunlight is made up ofseven colours named as violet,indigo, blue, green, yellow, orange and red. In short form, it is known as VIBGYOR (first letter ofevery colour) and the splitting of light into its constituent colours is known as dispersion of light.

Activity 8

Aim To observe the effect of light on the size of pupil.

Material Required A torch.

Procedure

1. Look into your friends eye and observe the size of pupil.
2. Now, throw light on her eye with the torch. Now, observe the size of pupil.
3. Now, switch OFF the light and observe the size of pupil once again.

Conclusion

1. Size of pupil is small when the torch is ON. This happens to protect eye from intense light.
2. Size ofpupil increases when the torch is switched off. This happens to gather more light to see objects clearly.

Activity 9

Aim To demonstrate the existence of blind spot in the eye.

Material Required A white paper strip and a marker.

Procedure

1. Make a round mark and a cross mark on a sheet of paper with the help of marker. The round mark should be or the right side of the cross mark.
2. Distance between the two marks should be 6-8 cm.
3. Now, hold this paper at an arm’s length from the eye.
4. Close your left eye and look continuously on the cross mark.
5. Move the sheet slowly towards your eye and keep your eye on the cross.
6. Move the sheet towards your eye until the round mark disappears.
7. Now, close your right eye and look at the round mark, then repeat step 5 and 6

Conclusion While bringing the strip towards the eye at some point, one mark disappears.

Activity 10

Aim To understand the persistence of vision.

Material Required A square piece of cardboard, a long thread and a pencil.

Procedure

1. Make two holes in the cardboard as shown in figure.
2. Draw a cage on one side of the cardboard and a bird on the other side of the cardboard.
3. Now, insert the string in the hole as shown in the diagram.
4. Now, hold the free ends of the thread on both sides and twist it in such a way that the cardboard rotates very fast. Now, write your observation.

Conclusion The bird appears as it is in the cage but it is on the other side of the cardboard.

CBSE Class 8 Science Chapter 13 Light Fill In The Blanks

Question 1. A person 1 m in front of a plane mirror seems to be ________ m away from his image.
Answer: 2

Question 2. If you touch your ________ ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with
Answer: left, left hand

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Question 3. The size of the pupil becomes ________ when you see in dim light.
Answer: large

Question 4. Night birds have ________ cones than rods in their eyes.
Answer: lesser

Question 4. The incident rayi the normal ray and the reflected ray, all lie in the ___________ plane.
Answer: same

Question 5. When the angle between plane mirrors is more than 90°, it forms ___________ images.
Answer: Two

Question 6. ___________ is The transparent part of the outermost layer of eye.
Answer: Comea

Question 1. _____________ reflection takes place from a smooth surface.
Answer: Regular

Question 2. _____________ is the defect in which a person can see nearby object very clearly but cannot see distant objects.
Answer: Myopia

Question 3. The minimum distant at which the eye can see object distinctly is _____________  for a normal person.
Answer:  25 cm

Question 4. The image of an object persists on the retina of an eye for about _____________ second even after the object has disappeared.
Answer: 1/16

Question 5. If the still pictures of a moving object are flashed on our eyes at a rate faster than _____________ pictures per second, the eye perceives the object as moving.
Answer: 16

Question 6. In a movie, the still pictures in proper sequence are projected on the screen usually at the rate of _____________ pictures per second.
Answer: 24

Class 8 Science Chapter 13 Light True or False

Question 1. Diffused/Irregular reflection takes place from rough surfaces.
Answer: True

Question 2. Diffused reflection gives a sharp image.
Answer: False

Question 3. Two mirrors inclined to each other give multiple images.
Answer: True

Question 4. An eye lens focuses light behind the eye on the cornea.
Answer: False

Question 5. The part of the eye that renders colour to it is the cornea.
Answer: False

Question 6. Cones and rods are the light-sensitive cells.
Answer: True

Question 7. Sunlight, called white light, consists of seven colours.
Answer: True

Question 8. Visually challenged people can read and write with a hearing aid.
Answer: False

Question 7. The law of reflection is not valid for rough surfaces.
Answer: False

Question 8. Periscope works on the multiple reflection by a plane mirror.
Answer: True

Question 9. Sunlight is a mixture of eight different colours.
Answer: False

Class 8 Science Chapter 13 Light Match The Columns

 Match Column 1 with Column 2.

Answer: 1. (a)-(2), (b)-(4), (c)-(5), (d)-(3), (e)-(1)

Assertion-Reason Questions

The following question consists of two statements: Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Question 1. Assertion (A) Irregular surfaces produce diffused reflection.

Reason (R) Due to failure of law of reflection, diffused reflection is produced.

Answer: 3. The law of reflection is followed by every surface but due to irregularities, some surfaces produce diffused reflection. Hence, A is true but R is false.

Question 2. Assertion (A) Night birds have more rods than cones.

Reason (R) Rods are more sensitive for dim light than cones.

Answer: 1. Night birds have more rods than cones because they are designed by nature to see in night. Hence, both A and R are true and R is the correct explanation of A.

Question 3. Assertion (A) Iris controls the size of lens.

Reason (R) Iris controls the amount of light entering in the eye.

Answer: 4.  Iris controls the size of pupil. Hence, A is false but R is true.

Question 4. Assertion (A) Eye sight becomes foggy in old ages.

Reason (R) Crystalline lens becomes milky and cloudy in old ages.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Assertion-Reason Questions

The following questions consists of two statementsAssertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below.

1. Both A and R arc true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Question 10. Assertion (A) Owl can see very-well In the night.

1. Reason (R) Owl has a large cornea and a large pupil to allow more light in its eye.
2. Answer: 1. Both A and R arc true and R is the correct explanation of A.
3. Question 11. Assertion (A) Rainbow is the natural phenomenon of multiple reflection.
4. Reason (R) Rainbow forms when sunlight falls on the rainwater droplets.

Answer: 4. A is false but R is true.

CBSE Chapter 11 Chemical Effects Of Electric Current Long Answer Type Questions

Question 1. Prove that lemon juice and vinegar are good conductors of electricity.
Answer: Take a few plastic or rubber cap bottles. Put a teaspoon of lemon juice or vinegar in one cap.

Read And Learn More CBSE Class 8 Science Long Answer Questions

Now, bring the tester over the cap and let the ends ofthe tester dip into lemon juice or vinegar. So, we can see that, bulb starts to glow. It indicates that lemon juice and vinegar are good conductors of electricity.

Question 2. You are provided with n magnetic compasses, an empty matchbox, a battery of two cells and connecting wires. Using these objects, how will you make a tester for testing an electric circuit? Draw the necessary circuit diagram and explain.

Answer: Take the tray from the inside of a discarded matchbox. Wrap an electric wire a few times around the tray. Place a small compass needle inside it. Now connect one free end of the wire to one terminal of a battery.

Leave the other end free. Take another piece of wire and connect it to the other terminal of the battery. Join the free ends of two wires momentarily.

The compass needle should show deflection. Your tester with two free ends of the wire is ready.

Question 3. Observing that the bulb does not glow in the circuit. Boojho changed the circuit. He observed deflection in the magnetic compass.

1. What does the deflection in the magnetic compass indicate?
2. Why did the bulb not glow in?
3. What would be the effect of an increase in the number of turns in the coil wound around the magnetic compass?

Answer:

1. The deflection in the magnetic compass shows that the current is flowing in the circuit.
2. The bulb did not glow, it may be because of the current passing through the circuit could be weak. Also, it may happen because ofother reasons like due to bulb fused or the connections may be loose.
3. An increase in the number of turns in the coil wound Around the magnetic compass would increase the magnetic field around the magnetic compass which will result in the increase in the deflection in the magnetic compass.

Question 4. One day Ram was performing an experiment. He was trying to design an electric circuit In which he Included tester, bulb and a battery.

He had so much eagerness regarding this experiment that, in much haste, he forgot to take the connecting wires of aluminium.

He took the wires without any coating of PVC on them, so it could be dangerous for him. Any how, he managed to design an electric circuit but the moment, he switched ON the circuit, a spark was produced and bulb got fused with a small sound.

He was about to touch those wires and heated bulb with his bare hands, at the same time, his teacher suggested him to perform the experiment by taking precautions. Explain what could have happened if Ram had touched the electric bulb with his bare hands.

Mention why he should use the aluminium wires in his experiment? State the values shown by Ram’s teacher here.

Answer: If Ram touched the heated electric bulb, then his hands could get a severe burn, and he would not be able to experiment again with the same desire.

He uses the aluminium wires in his experiment because aluminium is a good conductor of electricity.

Ram’s teacher has a great concern towards Ram, so that he can perform the experiment carefully and can get to its fruitful conclusion.

CBSE Class 8 Science Chapter 11 Chemical Effects Of Electric Very Short Answer Type Questions

Question 1. Will the solution of sugar in distilled water conduct electricity?
Answer: The sugar solution in distilled water will make it a good conductor of electricity, and current can easily pass through it.

Question 2. The fresh fruits and vegetables conduct electricity to some extent. Explain why
Answer: Due to the presence of various salt solutions in fruits and vegetables, they can conduct electricity to some extent.

Read And Learn More CBSE Class 8 Science Very Short Questions And Answers

Question 3. State, which one is a better conductor of electricity, sea water or drinking water?
Answer: As sea water contains more salt, which increases conductivity. So, sea water is a good conductor of electricity.

Question 4. Mention any one important difference in the conduction of electricity by solids over liquids.
Answer: Since, no chemical changes takes place when electricity is allowed to pass through the solids while in liquids chemical changes take place when electricity is passed through it.

Question 5. Name the effect of the current responsible for the glow of the bulb in an electric circuit.
Answer: The heating effect of electric current is responsible for the bulb to glow in an electric circuit.

Question 6. A chemical compound is produced by the method of electrolysis. Give an example.
Answer: Solution hydroxide or caustic soda is produced by the electrolysis of an aqueous solution (water solution) of sodium chloride.

Question 7. Mention the planner who should oversee the electroplating.
Answer: The waste of electrolysers should be disposed of far away from residential areas

Question 8. Why is tin electroplated on iron to make cans used for
Answer: Electroplating is done on the iron to prevent it from rusting and corrosion. By electroplating the iron with tin, the food does not come into contact with iron directly, so it is protected from getting spoiled.

Question 9. During the electrolysis of water, at which electrode is hydrogen gas evolved?
Answer: During the electrolysis of water, hydrogen gas is evolved at the cathode.

Question 10. Explain why a layer of zinc is coated over Iron?
Answer: A Layer of zinc is coated over iron because zinc prevents it from rusting and corrosion.

CBSE Class 8 Science Chapter 12 Some Natural Phenomena Short Answer Questions

Question 1. You might have observed on a dry day that when you touch the screen of a television or computer monitor (with a picture tube), you get a slight shock. Why does it happen?
Answer: It happens because the television screen or computer monitor is charged and has static charges. When we touch them with our hands, which are uncharged, the charges attract our hands and transfer through our hands, and we get a small shock.

Read And Learn More CBSE Class 8 Science Short Answer Questions

Question 2. In an electroscope, if a negatively charged body is brought in contact with the metal clip, the strips of the electroscope diverge. If another charged object carrying an equal amount of positive charge is brought in contact with the clip, what will happen?
Answer: As it is clear from the figure, whether we bring a positive or negative rod, the strips will always repel because an equal amount of charges are transferred to the strips, and like charges always repel each other.

Question 3. The strips of an electrosope diverge when a charged body is brought in contact with the Mental cup. Now, the clip is touched gently by our hand. What will happen to the strips? explain
Answer: If we touch the strip while standing on ground (not on any insulating base), the charges will pass through our hand to the ground because they will get the path to flow and strips will not diverge.

Question 4. During the construction of a building, the lightning conductor was left hanging in the air by mistake. Would the lightning conductor still be effective? Explain.
Answer: Lightning conductor will not work, it left hanging in the air because in order to work, it must be installed properly and grounded using any metal (copper) plate.

Question 5. Explain the concept of the lightning rod. Also, explain how it protects the buildings?
Answer: The device which is used to protect tall buildings from the effect of lightning is called lightning conductor. Also, metallic rod is installed in the walls of the buildings during its construction and one end of the rod is kept out in air and the other end is fixed in the ground. So, it provides an easy route for transfer ofelectric discharge to the earth.

Question 6. Identify the lightning conductor and the copper plate in the figure.

Answer:

Question 7. Give the name of the scientist who established the relation between sparks produced by amber and thunderstorms. Explain in brief.
Answer: There was an American scientist, Benjamin Franklin, who established that sparks produced by amber are similar to the sparks produced by thunderstorm. For this, he flew a kite tied with a silken thread which had an iron key attached to it on rainy day. So, during lightning, he experienced the shock through iron key, which proved that clouds also carried charges.

Question 8. If air and cloud are good conductors of electricity, do you think lightning could occur? Explain.
Answer: No, there will not be lightning at all because all the charges collected in the clouds will continuously transfer through the air, and there will be no lightning.

Question 9. Explain the electric discharge that occurs in clouds.
Answer: During thunder, negative charges accumulate near the clouds, and positive charges accumulate near the ground.

So, when these charges meet, then electric discharge takes place between ground and clouds. So a large amount of energy released in the form of thunder and lightning.

Question 10. If the materials used for constructing a building were good conductors, do you think lightning would strike the building? Will the lightning conductor still be required to be installed in the building?
Answer: Lightning will not strike the building in such a case because all the lightning striking the building will reside on the surface of the building. Now, there is no need to install any lightning conductor because all the work oflightning conductor is done by the conducting material itself.

Question 11. Mention three precautions that you will take to protect yourself if an earthquake strikes when you are
Answer: Three precautions during an earthquake inside the house are as follows

1. Instead of running away, we should get under a desk, table, or bench.
2. Pick a safe place where things will not fall on you, away from windows, bookcases or tall heavy furnitures.
3. Wait at your safe place until the shaking stops.

Question 12. Is it possible to predict the occurrence of an earthquake?
Answer: No, scientists have tried lots of different ways of predicting earthquake but none have been successful so far. They have a pretty good idea of where an earthquake is most likely to hit but they still cannot tell exactly when it will happen.

Question 13. What is an earthquake?
Answer: An earthquake is a sudden shaking or trembling of the earth that lasts for a very short time.

Question 14. What causes an earthquake?
Answer: The outermost layer of the Earth is fragmented. Each fragment is known as a plate. These plates are in continuous motion. When these plates collide with one another, they cause disturbance in the Earth’s crust. This disturbance shows up as an earthquake on the Earth’s surface.

Question 15. What could cause a disturbance inside the Earth?
Answer: The movement of tectonic plates, when it collide with one another, then it cause a disturbance inside the Earth.