Class 8 Science

Class 8 Science Chapter 11 Chemical Effects Of Electric Current Activity 1

Aim: To ensure that the tester is working properly.

Material Required: An Electric Bulb, a Battery, a metal water

Procedure:

1. Firstly, connect all the materials as shown in the figure to make a tester
2. Join the free ends of the tester together for a moment. This completes the circuit of the tester and observe it.
3. Now, if the bulb does not glow, it means that the tester
   is not working.
4. The reason behind this may be that the connections are loose or the bulb is fused, or the battery is used up.
5. Check whether all the connections are tight or not or replace the bulb and battery with another fresh bulb and battery.
6. Now check if the tester is working or not.

Conclusion: We have concluded that our tester is working. Now, we can use it to test the various liquids’ conductivity.

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Class 8 Science Chapter 11 Chemical Effects Of Electric Current Activity 2

Aim: To test the conduction of electricity in lemon juice or vinegar.

Material Required: A tester, a  few caps of plastic bottles, lemon juice or vinegar.

Procedure:

1. Firstly, collect a few small plastic caps from discarded bottles and clean them.
2. Now, put a teaspoon of lemon juice or vinegar in a plastic cap
3. Bring the tester over this beaker and let the ends of the tester dip into the lemon Juice or vinegar.
4. [Ensure that the ends should not be more than 1 cm apart
5. Observe the bulb, you will find that the bulb glows very dimly.

Conclusion: We have concluded that the liquid between the two ends of the tester allows the electric current to pass through it.

The dimly glowing bulb indicates that though vinegar or lemon juice conducts electricity but they are weak conductor of electricity.

Simple Electroplating Experiment For Class 8 With Copper Sulphate Solution Activity 3

Aim: To observe the conduction of electricity through different liquids by using another tester.

Material Required: A compass, different liquids like lemon juice, tap water, vegetable oil etc., an empty match box, two electric wires.

Procedure:

1. Firstly, take a cardboard tray from the inside ofa discarded match box and place a small compass inside it.
2. Now, wrap an electric wire around the cardboard tray and connect one free end to the terminal of a battery after leaving the other end free.
3. Take another piece of wire and connect it to the other terminal of the battery. Your tester is ready to use.
4. Now, repeat with the help of this tester. You will find a deflection in the compass needle when the free end of the tester is dipped in the lemon juice.

Repeat the Activity with other liquids such ns tap water, vegetable oil, milk, honey etc and observe the deflection. Remember to wash and wipe dry the ends of the tester afler testing each liquid.

In each case, observe whether the magnetic needle shows deflection or not. Record your observations in the table below.

Conclusion: We have concluded that some liquids are good conductors of electricity, whereas other liquids are poor conductors of electricity.

Chemical Effects Of Electric Current: All Activities Activity 4

Aim: To show that a poor conductor can be a good conductor under some conditions.

Material Required: Distilled water, common salt, tester, plastic cap of a discarded bottle.

Procedure:

1. Firstly, take some distilled water in a plastic cap.
2. Now, use the tester to check whether distilled water conducts electricity or not. You will find that no electricity is conducted by the distilled water.
3. Dissolve a pinch of common salt in distilled water and test the conductivity. You will find that electricity is conducting here.

Conclusion: We have concluded that, under some conditions poor conductor can become a good conductor of electricity.

Class 8 Science Chapter 11 Chemical Effects Of Electric Current Activity 5

Aim: To show that acid, base and salt solutions also conduct electricity.

Material Required: Three plastic caps of discarded bottles, distilled water, a tester, lemon juice, caustic soda, sugar.

Procedure

1. Take three clean plastic caps of discarded bottles and pour about two teaspoons of distilled water in each of them.
2. Add a few drops oflemon juice to distilled water in first cap. Similarly, add caustic soda and sugar to second and third cap, respectively.
3. Now, test which solution conducts electricity and which does not.

Conclusion: we have conclued that all the three solutions conduct electricity. It means that most of the liquids that conduct electricity are solutions of acids, bases and salts.

Class 8 Science Chapter 11 Chemical Effects Of Electric Current Activity 6

Aim: To demonstrate the chemical effects of electric current.

Material Required: A battery, copper wires, carbon rods, lemon juice, and water.

Procedure:

1. Firstly, take out carbon rods from two discarded cells. Clean their metal caps with sandpaper.
2. Now, wrap copper wires around the metal caps ofthe carbon rods and join them to a battery.
3. Now, put a cup of water in a beaker. Also, add a few drops of lemon juice to the water to make it more conducting.
4. Now, immerse the electrodes in this solution. Make sure that the metal caps of carbon rods are above the level of electrolyte in a beaker.
5. Wait for 3 to 4 minutes. Notice the electrode carefully, we will see that the bubbles of gases are produced at the two carbon electrodes.

Conclusion: We have concluded that, the chemical reaction has taken place in the solution, when electric current is passing through it.

Class 8 Science Chapter 11 Chemical Effects Of Electric Current Activity 7

Aim: To electroplate a metal object with copper. Material Required Copper sulphate, 250 ml. distilled water. dry beaker, copper plates.

Procedure:

1. Firstly, take copper sulphate and two copper plates of size around 10 cm x 4cm.
2. Now, take 250 mL of distilled water in a clean and dry beaker and dissolve two teaspoons of copper sulphate in it and add a few drops of dilute sulphuric acid to this solution to make it more conducting.
3. Now, clear the copper plates with sand paper and connect them to the terminals ofa battery and immerse them in copper sulphate solution.
4. Allow the current to pass for about 15 min.
5. Now, remove the electrodes from the solution and look at them carefully.

Conclusion: We have concluded that the copper metal gets transferred from the positive electrode to the negative electrode.

Chapter 11 Chemical Effects Of Electric Current Fill In The Blanks

Question 1. Materials which do not allow an electric current to pass through them are called_____________
Answer: Insulator

Question 2. Small amounts of a mineral salt present naturally in water makes it a _____________of electricity
Answer: Good Conductor

Question 3. LED glows even when an electric current passes through it
Answer: Small

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Question 4. If we pass current through a conducting solution, then
_____________effect takes place.
Answer: Chemical

Question 5. A liquid that conducts electricity due to the presence of ions is called_____________
Answer: Electrolyte

Question 6. The object to be electroplated is taken as_____________ electrode.
Answer: Negative

Question 7. One of the most common applications of the chemical effect of electric current is
Answer: Electroplating

Question 8. Electroplating is used to give more ______________ to the cheap objects.
Answer: Attraction/shining

Question 9. Electroplating of_____________ is done on objects like water taps and cycle bells to give them a shiny appearance.
Answer: Chromium

Question 4. LEDS glow if a longer lead is connected to the ________ terminal of the battery and the shorter lead is connected to __________terminal of the battery.
Answer: Positive, negative

Question 5. The deposition of a layer of gold on silver ornaments is known as __________
Answer: Eletroplating

Question 1. Most liquids that conduct electricity are solutions of ____________ and ____________ 
Answer: Acids, bases, salts

Question 2. The passage of an electric current through a solution causes ____________ effects.
Answer: Chemical

Question 3. If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the____________terminal of the battery.
Answer: Negative

Chapter 11 Chemical Effects Of Electric Current True/False

Question 1. Some liquids are good conductors of electricity, and some are poor conductors.
Answer: True

Question 2. Distilled water conducts the electric current.
Answer: False

Question 3. Adding sugar makes pure water conductive.
Answer: False

Question 4. Most liquids that conduct electricity are solutions of acids, bases, and salts.
Answer: True

Question 5. An electric bulb glows due to the chemical effect of electricity.
Answer: False

Question 6. The passage of an electric current through a conducting liquid causes chemical reactions.
Answer: True

Question 7. The chemical effect of electric current is used in the purification of salts.
Answer: False

Question 8. The chemical reaction brought about by an electric current may produce changes in the colour of solutions.
Answer: True

Question 9. Electrolysis is a chemical change.
Answer: True

Question 10. During the electrolysis of water, hydrogen gas is liberated at the anode.
Answer: False

Question 11. During electroplating, the object to be electroplated is made the anode.
Answer: False

Question 6. Due to the heating effect of the current, the bulb produces light.
Answer: True

Question 7. LEDs are not a better option than an electric bulb in a tester.
Answer: False

Question 8. Vegetable oil mixed with distilled water is a good conductor of electricity
Answer: False

Chapter 11 Chemical Effects Of Electric Current Match The Columns

Question 1. Match Column 1 with Column 2.

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

Chapter 11 Chemical Effects Of Electric Current: Assertion-Reason Questions

The following questions consist of two statementsAssertion (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) Pure water is a poor conductor of electricity.
Reason (R) Pure water contains many minerals that are beneficial for human health.

Answer: 3. A is true, but R is false.

Question 2.

Assertion (A) Water decomposes into hydrogen and oxygen on heating at high temperatures.
Reason (R) The Chemical effect of the current is used to decompose chemical compounds into their elemental form.
Answer: 2. A is false, but R is true.

The following questions consist of two statementsAssertion (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 3. 

Assertion (A) Sea water is a good conductor of electricity.
Reason (R) Sea water contains different types of salts.

Answer: Sea water contains different types of salts and Ions. These salts are responsible for conducting electricity. This is the reason that seawater is a good conductor of electricity.

Question 4.

Assertion (A) Distilled water is a poor conductor of electricity.
Reason (R) Distilled water contains a small amount of mineral salt, which makes it a poor conductor.

Answer: Distilled water is a poor conductor ofelectricity as it is free from mineral salts.

Question 5.

Assertion (A) A magnetic compass can be used in place of an electric bulb to make a tester.
Reason (R) A compass gets deflected when it is placed near a current-carrying conductor.

Answer: We can detect the presence of electric current with the help of magnetic compass. A compass starts deflecting when it is placed nearby a current carrying wire.

Question 6.

Assertion (A) Materials like wheel rims, handlebars of bicycles, etc, are coated with chromium metal to make it more shiny and attractive.
Reason (R) Chromium metal does not corrode and saves materials from scratches.

Answer: Chromium metal is less reactive. It does not corrode easily. That’s why materials like rims, handle of bicycles etc., arc coated with chromium metal.

CBSE Class 8 Science Chapter 10 Sound Multiple Choice Questions

Question 1. What is an example of an object that works on vibrations?

1. A spinning top
2. A coin is tossed
3. Marble rolling on a ramp
4. Guitar string being plucked

Answer: 4. Guitar string being plucked

Question 2. Which of the following statements is correct?

1. Sound is produced by vibrations.
2. Sound requires a medium for propagation.
3. Light and sound both require a medium for propagation.
4. Sound travels slower than light.

Choose the correct options 

1. 1 and 2
2. 1, 2, and 3
3. 2, 3, and 4
4. 1, 2, and 4

Answer: 4. 1, 2, and 4

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Question 3. Sound cannot travel through

1. Solid
2. Liquid
3. Air
4. Vacuum

Answer: 4. Vacuum

Question 4. A list of media is given below

1. Wood
2. Water
3. Air
4. Vacuum

Answer: 2. Water

Question 5. In which of these media can sound travel?

1. 1 and 2
2. 1, 2, and 3
3. 3 and 4
4. 2, 3, and 4

Answer: 3. 3 and 4

Question 6. Which option explains how sound is produced by the voice box in the human throat?

1. The voice box vibrates due to the air coming out of the lungs
2. The vocal cords vibrate due to the air coming in through the voice box
3. The vocal cords stretched across the voice box are vibrated by air coming from the lungs
4. The stretched vocal cords across the voice box produce the air to vibrate the voice box

Answer: 3. The vocal cords stretched across the voice box are vibrated by air coming from the lungs

Question 7. What is the structure of the eardrum?

1. It is the stretched cord in the ear
2. It is the stretched membrane in the car
3. It is the nerve that transmits a signal to the brain
4. It is the funnel-type canal of lie ear through which sound enters

Answer: 2. It is the stretched membrane in the car

Question 8. Is equal to

1. 1 vibration per minute
2. It’s vibrations per minute
3. 60 vibrations per minute
4. 600 vibrations per minute

Answer: 3. 60 vibrations per minute

Question 9. An object is vibrating at 5 Hz. What is its period?

1. 0.02 s
2. 0.2 s
3. 2 s
4. 20.0 s

Answer: 1. 0.02 s

Question 10. The loudness of sound depends on its

1. Amplitude
2. Period
3. Frequency
4. Speed

Answer: 1. Amplitude

Question 11. To reduce the loudness of a sound, we have to Competency-Based

1. Decrease Its Frequency Of Vibration Of The Sound
2. Increase Its Frequency Of Vibration Of The Sound
3. Decrease Its Amplitude Of Vibration Of The Sound
4. Increase Its Amplitude Of Vibration Of The Sound

Answer: 3. Decrease Its Amplitude Of Vibration Of The Sound

Question 12. Sound can travel through

1. Gases Only
2. Solids Only
3. Liquids Only
4. Solids, Liquids, And Gases

Answer: 4. Sound can travel through solids, liquids, and gases, but it cannot travel in a vacuum.

Question 13. Of which of flic following is likely to have the minimum frequency?

1. Baby girl
2. Baby boy
3. A man
4. A woman

Answer: 3. The Voice of a man is likely to have a minimum frequency.

The frequency determines the pitch of a sound; like the frequency of vibration is higher, the sound is and has higher the pitch. If the frequency of vibration is lower, the sound has a lower pitch.

CBSE Class 8 Science Chapter 10 Sound Long Answer Questions

Question 1. Anjali’s grandfather was talking to her about the quality of sound produced by different musical instruments. The instruments like sitar, harmonium, flute, etc., give us a pleasant sensation of hearing. The dholak on the other side creates a noise.

1. Mention the name of the vibrating part of the sitar.
Answer: The String of the sitar is a vibrating part of the sitar.

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2. Briefly explain how the loudness is created by the dholak.
Answer: If we beat the dholak, then the membrane of the dholak starts vibrating with high amplitude, and as a fact, the loudness is directly proportional to the square of the amplitude. Therefore, in the form of the loudness is created by beating the dholak.

3. We hear a shrilling sound from the flute. Explain why?
Answer: The sound wave produced by the flute is regularly curving, so there is no part of the noise. Thus, we hear the shrilling sound of the flute.

4. Mention the values displayed by Anjali’s grandfather.
Answer: The values displayed by Anjali’s grandfather are scientific methods and critical thinking.

Question 2. A pendulum oscillates 40 times in 4s. Find its time and frequency.
Answer:

Given, number of oscillations =40
Time token =4 s

As we know, the number of oscillations per second is the frequency.

⇒ \(\text { Frequency }=\frac{\text { Number of oscillations }}{\text { Time taken }}\)

⇒ \(=\frac{40}{4}=10 \mathrm{~Hz}\)

Time period \(=\frac{1}{\text { Frequency }}\)

⇒ \(=\frac{1}{10}=0.1 \mathrm{~s}\)

Question 3. Sketch, explain its functions in your own words
words.
Answer: In humans, the sound is produced by the voice box, also called the larynx. We can easily feel this part of the body by putting our lingers on the throat and find a hard hump tluit seems to move when we swallow.

1. Structure
2. It is the upper end of the windpipe.
3. Two vocal cords are stretched across the voice box or larynx.
4. The vocal cords are stretched in such a manner that it leaves a narrow slit between them for the passage of air.
5. Working
6. When the lungs force air through the slit, the vocal cords vibrate and hence, produce sound.
7. Muscles attached to the vocal cords can make the cords tight or loose.
8. When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose.

Question 4. Aditi hangs four steel dishes of the same size but different thickness. She hits each of them with an iron rod.

Based on the above picture, answer the following questions. The thicker the dish, the lower the vibration will be. Which dish will produce the loudest sound when hit?

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

Answer: 3. Dish 1

Which of these statements proves that sound can travel through solids?

1. We can hear the sound of the wind.
2. We can hear the sound of lightning.
3. We can hear a bell ringing from a distance.
4. We can hear heartbeats by using a stethoscope.

Answer: 2. We can hear the sound of lightning.

Which part of the human ear vibrates on receiving sound waves?

1. Ear Lobe
2. Eardrum
3. Inner Ear
4. Ear Canal

Answer: 3. Inner Ear

Question 5. Raghav kept a mini sound player in each of the two similar containers. He then tightly covered both containers with stretched plastic sheets. He placed some tiny rubber beads on the surface of the sheets. The picture shows what Raghav noticed when he turned ON the sound player.

1. Which of these questions can be answered using the result of Raghav’s activity?

1. Does sound travel as waves?
2. Does it sound product vibration?
3. Does sound travel through a vacuum?
4. Does sound travel faster in solids than in gases?

Would the result of Raghav’s activity change if fewer beads had been used? Explain your answer.

2. The picture shows four sound waves

Based on the above picture, answer the following questions

1. Which sound wave has the highest pitch?
Answer: 1-b 2. The number of beads will not change the result activity because the vibration of the plastic sheet depends on the sound.

2. Which of these is true about the four sound waves?
Answer: High frequency produces high pitch. Hence, wave 2 has the highest pitch.

(a) Yes (b) Yes (c) No

CBSE Class 8 Science Chapter 10 Sound Short Answer Questions

Question 1. Suppose a stick is struck against a frying pan in a vacuum. Will the frying pan vibrate? Will we be able to hear the sound? Explain.
Answer: Yes, the flying pan will vibrate. Since, It Is being hit by the stick hut vibrations need .1 medium to travel, and there is no medium in a vacuum, so we cannot hear the vibrations produced.

Question 2. A stretched string, when set into vibration, produces the audible sound. Explain how?
Answer: A stretched string, on being set into vibration, forces the surrounding air to vibrate. This vibrating air in them affects our eardrum and produces an audible sound.

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Question 3. Astronauts in outer space have to use radios to communicate with one another. Why?
Answer: In outer space, there is no medium to help transmit sound. To communicate with one another, astronauts make use of electromagnetic waves such as radio waves, which can travel througha  vacuum.

Question 4. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
Answer: No, they cannot talk to each other without using any special device because there is no medium in space, and sound needs a medium to travel.

Question 5. The sound produced by a mosquito is quite different from the roar of a lion. Explain the distinguishing points along with the reason.
Answer: A mosquito produces sound by the vibration of its wings in open air, while the lion roars by the vibration of its vocal cords.

Due to this, the amplitude of the sound produced by a mosquito will be less than the sound produced by a lion, and even the pitch and quality of the two sounds are different, which makes the two sounds different and distinguishable.

Question 6. Explain the process, which bats use ultrasonic waves to catch prey.
Answer: The ultrasonic waves produced by the bats are high-pitched pitched are not heard by human beings. So, these ultrasonic waves, after striking the insect, send back an echo which is heard by the bat, and finally it gets over to the insect and catches it.

Question 7. Last Monday, Anita and her parents were going to the market by an auto rickshaw. On her way while taking a left turn, they heard the horn of a speeding truck towards the turn. Suddenly, the auto rickshaw driver stopped his vehicle by applying the brakes. Thus, by adopting the precautionary measure of blowing the horn, the truck driver saved lives.

• The loudness of a horn depends on what factor?
• Mention the values displayed by both the drivers

Answer: The factor on which the loudness of a horn sound depends is the amplitude of vibration of the horn.

The values displayed by both drivers are awareness and sensitivity.

Question 8. We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us.
Answer: that the range of vibrations is different for different objects. But we can only hear the vibrations which lie between 20 Hz to 20000 Hz, so the sound of every vibration cannot be heard by us.

Question 9. We have a stringed musical instrument. The string is plucked in the middle first with a force of greater magnitude and then with a force of smaller magnitude. In which case would the instrument produce a louder sound?
Answer: It will create more louder sound in case the string is stretched with a greater force because the amplitude is greater in this case, and loudness depends on the amplitude. The greater the loudness, the greater will be the amplitude.

Question 10. A simple pendulum makes 10 oscillations in 20 s. What is the period and frequency of its oscillations?
Answer: Given, number of oscillations =10

Time taken = 20 s

As we know, the number of oscillations per second is the frequency

⇒ \(\begin{aligned}
\text { Frequency } & =\frac{\text { Number of oscillations }}{\text { Time taken }} \\
& =\frac{10}{20}=0.5 \mathrm{~Hz}
\end{aligned}\)

⇒ \(\text { Time period }=\frac{1}{\text { Frequency }}=\frac{1}{0.5}=2 \mathrm{~s}\)

Question 11. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier, and thunder is heard later. Can you explain why?
Answer: Lightning is seen earlier than the sound of thunder because light travels faster than sound. Hence, it reaches us before the sound does.

Simple Sound Wave Experiment For CBSE Class 8 Science Project Activity 1

Aim: To understand how sound is produced by a metal. Material Required: A metal plate (like a pan) and a stick.

Procedure:

Take the metal plate and hang it at a convenient place in such a way that it does not touch any object.

1. Now strike it with the stick. You will hear a sound.
2. Now, touch the pan gently with your finger. You will feel some vibrations.
3. Again, strike the pan with the stick and hold the pan tightly. Now, you will not be able to hear any sound.
4. When the plate stops producing sound, touch it again. You will find no metal plate.

Conclusion: Sound is produced when the metal pan vibrates.

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Vibrating Ruler Frequency Experiment Class 8 Sound Chapter Activity 2

Aim: To produce sound with a rubber band.

Material Required: A pencil box, a rubber band, and two pencils.

Procedure:

1. Take the rubber band.
2. Wrap it around the longer side ofthe geometry box

Now, insert two pencils between the box and the 15  stretched rubber as shown in the figure.

Pluck the rubber band somewhere in the middle and observe the sound. You will find that the band starts vibrating and gives rise to sound.

Conclusion: Vibrating rubber band produces sound.

Amplitude And Frequency Demonstration Activity Class 8 Activity 3

Aim: To find the connection between sound and vibration. Material Required: A metal dish, water, and a spoon.

Procedure:

1. Pour some water into the metal dish.
2. Now, strike the edge of the dish with the spoon. You will hear some kind of sound.
3. Again, strike the dish and then touch it. You will feel some vibrations.
4. Strike the dish again and observe the surface of the water. You will observe waves on the surface of water.
5. Now, hold the dish and note the change in waves of the water surface. You will observe that waves disappear.

Conclusion

1. Water waves are visible until the sound is produced by the dish.
2. Water waves disappear when the dish stops vibrating

Noise Pollution Measurement Activity For Class 8 Students Activity 4

Aim: To identify the vibrating part of the musical instrument ektara.

Material Required: A hollow coconut shell, a thick wood strip, and a strong steel string.

Procedure:

1. Make a musical instrument, ekara, as shown in the diagram.
2. Play this instrument and identify the vibrating part.

Conclusion: The vibrating part in the ektara is the string

Comparing Loudness And Pitch Activity CBSE Class 8 Activity 5

Aim: To make a jaltarang at home.

Material Required: 6-8 bowls or tumblers, water, and a pencil.

Procedure:

1. Fill all the tumblers with water. The water level of all tumblers should be different.
2. Now, take the pencil and strike all the tumblers one by one. You will hear different sounds.

Conclusion: As the amount of water in the tumbler goes on increasing, the frequency of sound produced also goes on increasing. Hence, we hear a pleasant sound.

Class 8 Science Sound Mind Map Creation Activity Activity 6

Aim: To demonstrate the working of vocal cords to produce sound.

Material Required: Two rubber bands and paper.

Procedure:

1. Place the rubber strips one above the other and stretch them tight.
2. Now, blow air through the gap between them. Observe the sound produced.
3. Now, take the piece ofpaper with a narrow slit.
4. Hold it between your fingers and blow’ through the slit. Observe the sound produced.

Conclusion: Vocal cords also produce sound in the same When air passes through the vocal cords, it produces sound.

Sound Chapter Class 8 Lab Manual Activities With Observations Activity 7

Aim: To show that sound needs a medium to travel.

Material required: Metal or glass tumbler and a cell phone.

Procedure:

1. Place the cell phone into the tumbler.
2. Ask your friend to give a ring on this cell phone from another cell phone.

1. Listen to the ring carefully.
2. Now, surround the rim of the tumbler with your hands. Put your mouth on the opening between your hands.
3. Indicate to your friend to give a ring again.
4. Listen the ring while sucking air from the tumbler.
5. You will observe that the sound becomes fainter.
6. Remove the tumbler from your mouth and again notice the loudness of the sound.
7. Conclusion: Sound requires a medium to travel.

Class 8 Science Sound Activity-Based Learning Questions Activity 8

Aim: To show that sound travels through liquid. Material required: A bucket or bath tub, clean water, and a small bell.

Procedure:

1. Fill the bathtub with clean water.
2. Take the small bell in one hand and shake this bell inside the water.
3. Make sure that the bell does not touch the body of the bathtub.
4. Place your ear gently on the water surface. Take care that water should not enter the ear. Try to listen to the sound of the bell.

Conclusion: Sound can travel through liquid.

CBSE Class 8 Science Chapter 10 Sound Fill In The Blanks

Question 1. Sound is produced by__________ objects.
Answer: Vibrating

Question 2. The other name of human voice box is__________
Answer: Larynx

Question 3. Sound can travel in and __________
Answer: Solids, liquids, gases

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Question 4. The loudness of normal breathing of humans is__________ dB.
Answer: 10

Question 5. Vibration is repeated__________ and motion.
Answer: To, From

Question 6. A tight membrane vibrates at a much__________ frequency than a loose one.
Answer: Higher

Question 7. Sound which is pleasing to our ears is called__________
Answer: Music

Question 8. A person having partial hearing loss can hear properly by using a device called__________ aid.
Answer: Hearing

Question 9. The speed of sound in air is__________
Answer: 344m/s

Question 10. Muscles attached to the vocal cords can make the cords ___________or__________
Answer: Tight, loose

Question 11. The pitch of the sound depends on the_____________
Answer: Frequency

Question 12. The time taken by an object to complete one oscillation is called
Answer: Period

Question 13. The amount of vibration determines loudness.
Answer: Amplitude

Question 14. The unit of frequency is
Answer: Hertz

Question 15. Unwanted sound is called
Answer: Noise

Question 16. The frequency of vibration determines the Shrillness of a sound.
Answer: Frequency 

Class 8 Science Chapter 10 Sound True Or False

Question 1. The intensity of the sound depends on the frequency of the wave.
Answer: True

Question 2. In human beings, the vibration of the vocal cords produces sound.
Answer: True

Question 3. The higher the amplitude of vibration, the lower the pitch.
Answer: False

Question 4. Regular vibrations produce musical sounds.
Answer: True

Question 5. Shriller sound has a higher frequency.
Answer: True

Question 6. Plantation along the roadside can reduce noise pollution.
Answer: True

Question 7. Man cannot hear the sound of bats.
Answer: True

Question 7. The speed of sound is more than the speed of light.
Answer: False

Question 8. The sound travels fastest in solids.
Answer: True

Question 9. The sound waves produced by the bats are infrasonic.
Answer: False

Question 10. Sound cannot travel in a vacuum.
Answer: True

Question 11. The number of oscillations per second of a vibrating object is called its period.
Answer: False; The number of oscillations per second of a vibrating object is called frequency.

Question 12. If the amplitude of vibration is large, the sound is feeble.
Answer: False; Amplitude of vibration is directly proportional to the loudness of sound.

Question 13. For human ears, the audible range is 20 Hz to 20000 Hz.
Answer: True

Question 14. The lower the frequency of vibration, the higher the pitch.
Answer: False; The lower the frequency of vibration, the lower the pitch.

Question 15. Unwanted or unpleasant sound is termed as music.
Answer: False; Unwanted or unpleasant sound is termed as noise.

Question  16. Noise pollution may cause partial hearing impairment.
Answer: True

Class 8 Science Chapter 10 Sound Match The Columns

Answer: 1-3, 2-3,3-1,4-5,5-4

Class 8 Science Chapter 10 Sound

The following questions consist of two statements- Assertion (A) and Reason (R). Answer these questions by selecting the appropriate options 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 10.

Assertion (A) Sound travels more slowly through liquid than.
Reson (R) Thu moloculon In farther from onch other.

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

Question 11.

Assertion (A): The sound of women is shriller than that of men. Ronson (R) The pitch of the sound depends on the frequency of the sound.
Answer: 2. Both A and R are true, but R is not the correct explanation of A.

The following questions consist of two statementsAssertion (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) Astronauts in space can hear each other. Reason (R) Loud sounds have high amplitude.
Answer: 4. A is false because sound needs a medium to travel, but there is no medium in space. R is correct. Hence, the correct option is (d).

Question 2. Assertion (A) Tabla, sitar, flute, and harmonium are musical instruments. Reason (R) Sound is produced by vibrations in musical instruments.
Answer: Both A and R are correct because, without vibration, sound cannot be produced. Hence, the correct option is (a).

Question 3. Assertion (A) Frequency is measured in hertz (Hz). Reason (R) Lower the frequency, the higher the pitch of
The sound.
Answer: R is false because for higher frequency pitch of the sound is higher. Hence, the correct option is (c).

Question 4. Assertion (A) Human beings cannot hear sounds less than 20 Hz. Reason (R)The  Audible range of humans is 20 Hz to 20 KHz.
Answer: The audible range of sound for human beings is indeed from 20 Hz and 20 kHz. So, both A and R are correct, and R is the correct explanation. Hence, the correct option is (a).

CBSE Class 8 Science Chapter 9 Friction Multiple Choice Questions

Question 1. In the figure, a boy is shown pushing the box from right to left.

The force of friction will act on the box

1. From right to left (←)
2. From left to right (→)
3. Vertically downwards (↓)
4. Vertically upwards (↑)

Answer: 2. From left to right (→)

Read And Learn More CBSE Class 8 Science Multiple Choice Questions

Question 2. To sharpen the blade of a knife by rubbing it against a surface, which of the following will be most suitable?

1. Stone
2. Plastic block
3. Wooden block
4. Glass block

Answer: 1. Stone

Question 3. A toy car released with the same initial speed will travel the farthest on

1. Muddy Surface
2. Polished Marble Surface
3. Cemented Surface
4. Brick Surface

Answer: 2. Polished Marble Surface

Question 4. A boy rolls a rubber ball on a wooden surface. The ball travels a short distance before coming to rest. To make the same ball travel a longer distance before coming to Rest he may

1. Spread a carpet on the wooden surface
2. Cover the ball with a piece of cloth
3. Sprinkle talcum powder on the wooden surface
4. Sprinkle sand on the wooden surface

Answer: 3. Sprinkle talcum powder on the wooden surface

Question 5. It is difficult to walk on a well-polished floor because the friction between our feet and the floor is

1. Increased
2. Reduced
3. Same
4. None of these

Answer: 2. Reduced

Question 6. A student wants to move a heavy block from one place to another. What method should the student apply to reduce the effort?

1. Pull the block using a rope
2. Place wheels under the block
3. Slide the block along the surface
4. Apply oil to the bottom of the block

Answer: 2. Place wheels under the block

Question 7. The picture shows four types of shoe soles.

Which shoe sole provides the best grip and friction while walking?

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

Answer: 4. Sole 4

Question 8. We can increase the friction by

1. Polishing
2. Making grooves and treads
3. Streamlining
4. Using a ball bearing

Answer: 2. Making grooves and treads

Question 9. If we apply oil to the door hinges, the friction will

1. Increase
2. Decrease
3. Disappear altogether
4. Will remain unchanged

Answer: 2. Decrease

CBSE Class 8 Science Chapter 9 Friction Multiple Choice Questions

Question 10. Fine powder is poured on the carromboard to

1. Increase Friction
2. Decrease Friction
3. Both (a) and (b)
4. None of these

Answer: 2. Decrease Friction

CBSE Class 8 Science Chapter 9 Friction Long Answer Questions

Question 1. Raju wanted to find out which one of the four surfaces produces the greatest friction. He pushed the same toy car on the four surfaces, separately.

Raju noted the distance travelled by car on each surface before stopping.

1. On which surface did the car experience the greatest friction?

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

Answer: 3. Surface 3

2. What must be kept the same in the activity to compare the distances travelled by the car?
Answer: The Toy car and pushing force must be kept the same in the activity to compare the distance travelled by the car.

Read And Learn More CBSE Class 8 Science Long Answer Questions

3. What will happen to the car if it continues to move on the surface for 1 h?

1. The wheels will get hard.
2. The wheels will become hot.
3. The wheels will shrink in size.
4. The wheels will change shape

Answer: 2. The wheels will become hot.

Question 2. The picture shows four different rubber tubes.

1. Which tube will experience the least friction while rolling on a surface? Explain your answer.
Answer: Tube 2 experiences the least friction while rolling on n surface because the area of contact between the two surfaces is less in the case of Tube 2.

2. Which of these would affect the amount of friction generated on a moving object? Circle ‘Yes’ or ‘No’ for the correct response.

Answer: (a) Yes, (b) Yes, (c) Yes

Question 3. Anshu lets a marble roll freely on four rough wooden planks. The table shows the time taken by the marble to reach the bottom of each plank.

1. What could be the value of X in the table?

1. 2s
2. 3s
3. 4s
4. 5s

Answer: 4. 5s

2. Anshu polished all four planks to smooth the surfaces. She repeated her activity on the polished planks. Will there be any change in the results? Explain your answer.

Answer: Yes, results will change. Polishing the surface makes it smooth, then the friction between the marble and the plank decreases, which results in a decrease in the time taken by the marble to reach the bottom.

CBSE Class 8 Science Chapter 9 Friction Short Answer Questions

Question 1. Imagine that an object is falling through a long, straight glass tube held vertically, and air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?
Answer: No, the object will not experience any frictional force because to experience the force of friction, two surfaces must be there, and there is only one surface in this case.

Question 2. While travelling on a rickshaw, you might have experienced that if the seat cover is very smooth, you tend to slip when the brakes are applied suddenly. Explain.
Answer: If the seat cover of the rickshaw is very smooth, then the friction between our body and he seat is very small. Therefore, when the brakes are applied, we tend to slip.

Read And Learn More CBSE Class 8 Science Short Answer Questions

Question 3. Two boys were riding their bicycles on the same concrete road. Ono has new tires on his bicycle, while the other has tires that are old and used tires. Which of them is more likely to slip while moving through a patch of the road that has lubricating oil spilled over it?
Answer: The hoy having tyres which are old and worn tires are most likely to slip because they will experience less frictional force, which is insufficient to move on the oily road.

Question 4. Explain why

1. A pencil will write on paper but not on glass.
Answer: Since, due to friction, a pencil writes on paper, but there is smoothness on the surface of glass, a pencil cannot write on glass.

2. Climbing a greasy pole is very difficult.
Answer: If a pole is polished with grease, then the surface of pole becomes smoother thus reducing friction. So, climbing a greasy pole becomes tough.

Question 5. The handle of a cricket bat or a badminton racket is usually rough. Explain the reason.
Answer: The handle of a cricket bat or badminton racquet is rough, so that while playing, the bat or badminton racquet does not slip away from the hands of the player. Roughness is responsible for the frictional force, without which gripping is not possible.

Question 6. Is there a force of friction between the wheels of a moving train and the iron rails? If yes, name the type of friction. If an air cushion can be introduced between the wheel and the rail, what effect will it have on the friction?
Answer: Yes, there is always a force of friction between the wheels of a moving train and the iron rails. The name of this friction is rolling friction, since the wheels are rolling on the track. On introducing an air cushion, the frictional force becomes less, since there is no contact between the rails and wheels.

Question 7. A father and son pushed their car to the side of the road as it had stalled in the middle of the road. They experienced that although they had to push with all their might initially to move the car, the push required to keep the car rolling was smaller once the car started rolling. Explain.
Answer: When the car is at rest, we have to apply a greater force because the value of static friction is greater. As the car starts moving, the friction changes into rolling friction, which is always less than the previous one. So, we have to exert a lesser force to keep it in motion.

Question 8. When the cutting edge of a knife is put against a fast-rotating stone to sharpen it, sparks are seen to fly. Explain the reason.
Answer: Due to the friction between the knife and the stone, the temperature of the knife and hence the stone increases, and it increases to such a level that sparks are produced, which can be seen while sharpening it.

Question 9. Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?
Answer: Cartilage present in the joints ofour body reduces friction during the movement of joints. But on wearing off this cartilage, the force of friction increases, due to which the smoothness of movement decreases, and one feels joint pain.

Question 10. Explain why the surface of the mortar and pestle (silbatta) used for grinding is etched again after prolonged use.
Answer: After prolonged use, the mortar and pestle loose their roughness, due to which frictional force reduces and it does not work properly. So, we have to etch it to make it rough again.

Question 11. You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.
Answer: It is due to the continuous rubbing of the soles with the ground; the spikes on the soles get damaged slowly, and the soles become slippery.

Question 12. Explain which principle Is Involved in machine belts.
Answer: In many machines (like flour mills), belts are used to drive wheels for running the machines. Greater friction is required between the belts and machine wheels, so that the belts can drive the machine wheels properly without slipping off the wheels. So, to increase friction, machine belts are made up of special materials having rough surfaces.

Question 13. A marble is allowed to roll down an inclined plane from a fixed height. At the foot of the inclined plane, it moves on a horizontal surface (a) covered with silk cloth, (b) covered with a layer of sand, and (c) covered with a glass sheet. On which surface will the marble move the shortest distance? Give a reason for your answer.

Answer: Marble will move the shortest distance on the layer of sand because it will exert a greater force of friction on the marble and other two surfaces like silk cloth and glass sheet will exert a lesser friction force comparatively.

Question 14. While playing tug of war, Preeti felt that the rope was slipping through her hands. Suggest a way out for her to prevent this.

Answer: To prevent slipping of the rope from hands, Preeti has to make her hands somewhat non-smooth, so she can rub her hands by introducing sand between them.