NCERT Solutions Class 8th Science Chapter – 13 Sound
| Textbook | NCERT |
| Class | 8th |
| Subject | Science |
| Chapter | 13th |
| Chapter Name | Sound |
| Category | Class 8th Science |
| Medium | English |
| Source | Last Doubt |
NCERT Solutions Class 8th Science Chapter – 13 Sound
?Chapter – 13?
✍Sound✍
?Question & Answer?
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 1 Question 1. Choose the correct answer. |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 2 Question 2.Voice of which of the following is likely to have a minimum frequency? |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 3 Question 3.In the following statements, tick ‘T’ against those which are true and ‘F’ against those which are false. 1. Sound cannot travel in a vacuum.
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| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 4 Question 4.Fill in the blanks with suitable words. 1. Time taken by an object to complete one oscillation is called _______ |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 5 Question 5.A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
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| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 6 Question 6.The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
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| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 7 Question 7.Identify the part which vibrates to produce sound in the following instruments. 1. Dholak 2. Sitar 3. Flute |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 8 Question 8.What is the difference between noise and music? Can music become noise sometimes? |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 9 Question 9.List the sources of noise pollution in your surroundings.
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| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 10 Question 10.Explain in what way noise pollution is harmful to humans. |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 11 Question 11. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer. |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 12 Question 12. Sketch the larynx and explain its function in your own words. |
| NCERT Solutions Class 8th Science (Chapter – 13) Question No – 13 Question 13. 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? |
Activities Solved
| Activity 1 Take a metal plate (or a shallow pan). Hang it at a convenient place in such a way that it does not touch any wall. Now strike it with a stick (Fig. 13.1). Touch the plate or pan gently with your finger. Do you feel the vibrations? Again strike the plate with the stick and hold it tightly with your hands immediately after striking. Do you still hear the sound? Touch the plate after it stops producing sound. Can you feel vibrations now?  ?♂️Answer: When we touch the pan gently with our finger after striking we feel the vibration. When we hold the pan tightly after striking it, we do not hear the sound. When the pan stops producing sound it also stops vibrating. Thus, we can conclude that the vibrating body produces sound. |
| Activity 2 Jake a rubber band. Put it around the, the longer side of a pencil box (Fig. 13.2). Insert two pencils between the box and the stretched rubber. Now, pluck the rubber band somewhere in the middle. Do you hear any sound? Does the band vibrate?  ?♂️Answer:Yes, we hear the sound on plucking the rubber band. Also, we find that the band is vibrating. Thus, all vibrating bodies produce sound. |
| Activity 3 Take a metal dish. Pour water into it. Strike it at its edge with a spoon (Fig. 13.3). Do you hear a sound? Again strike the dish and then touch it. Can you feel the dish vibrating? Strike the dish again. Look at the surface of the water. Do you see any waves there? Now hold the dish. What change do you observe on the surface of the water? Can you explain the change? Is there a hint to connecting sound with the vibrations of a body?  ?♂️Answer: On striking the metal dish we hear sound and on touching it we feel the dish vibrating. Striking the dish with water we see circular waves are produced. Thus vibrating object produces sound. |
| Activity 4 Take a hollow coconut shell and make a musical instrument ektara. You can also make it with the help of an earthen pot (Fig. 13.4). Play this instrument and identify its vibrating part.  ?♂️Answer: We observed that the vibrating part of the musical instrument ektara is stretched string. |
| Activity 5 Take 6-8 bowls or tumblers. Fill them with water up to different levels, increasing gradually from one end to the other. Now take a pencil and strike the bowls gently. Strike all of them in succession. You will hear pleasant sounds. This is your Jaltarang (Fig. 13.5).  ?♂️Answer: We can hear a pleasant sound. This is due to different levels of water in the bowls.Thus, we find that the shorter the length of the vibrating air column, the higher the pitch of the sound produced. |
| Activity 6 Take two rubber strips of the same size. Place these two pieces one above the other and stretch them tight. Now blow air through the gap between them [Fig. 13.6(a)]. As the air blows through the stretched rubber strips, a sound is produced. You can also take a piece of paper with a narrow slit and hold it between your fingers as shown in [Fig. 13.6(b)]. Now blow through the slit and listen to the sound.  ?♂️Answer: This activity shows that vocal cords also produce sound in a similar manner when they vibrate. |
| Activity 7 Take a metal or glass tumbler. Make sure that it is dry. Place a cell phone in it. Ask your friend to give a ring on this cell phone from another cell phone. Listen to the ring carefully. Now, surround the rim of the tumbler with your hands (Fig. 13.7). Put your mouth on the opening between your hands. Indicate to your friend to give them a ring again. Listen to the ring while sucking air from the tumbler. Does the sound become fainter as you suck air? Remove the tumbler from your mouth. Does the sound become loud again?  ?♂️Answer: We observed that sound becomes fainter than earlier when we try to suck air. But when we remove the tumbler from our mouth the sound again becomes loud. Thus, sound needs a medium to travel. |
| Activity 8 Take a bucket or a bathtub. Fill it with clean water. Take a small bell in one hand. Shake this bell inside the water to produce sound. Make sure that the bell does not touch the body of the bucket or the tub. Place your ear gently on the water surface (Fig. 13.8). Can you hear the sound of the bell? Does it indicate that sound can travel through liquids?  ?♂️Answer: We can hear the sound of the bell which indicates that sound can travel through liquids. |
| Activity 9 Take a metre scale ora long metal rod and hold its one end to your ear. Ask your friend to gently scratch or tap at the other end of the scale (Fig. 13.9). Can you hear the sound of the scratching? Ask your friends around you if they were able to hear the same sound?  ?♂️Answer: Yes, we find that we can hear the sound of the scratch. But, the people standing around us cannot hear the same sound or we can say that it is limping not audible to them. |
| Activity 10 Take a plastic or tin can. Cut its ends. Stretch a piece of rubber balloon across one end of the can and fasten it with a rubber band. Put four or five grains of dry cereal on the stretched rubber. Now ask your friend to speak” Hurrey, Hurrey” from the open end (Fig. 13.10). Observe what happens to the grain. Why does the grain jump up and down?  ?♂️Answer: The grain jump up and down because of the vibration caused underneath the stretched rubber. Thus when sound waves fall on the eardrum, it starts vibrating back and forth rapidly. |
| Activity 11 Take a metallic tumbler and a tablespoon. Strike the tablespoon gently at the brim of the tumbler. Hear the sound produced. Now bang the spoon on the tumbler and hear the sound produced again. Is the sound louder when the tumbler is struck hard? Now suspend a small thermocol ball touching the rim of the tumbler (Fig. 13.11). Vibrate the tumbler by striking it. See how far the ball is displaced. The displacement of the ball is a measure of the amplitude of vibration of the tumbler. Now, strike the tumbler gently and then with some force. Compare the amplitudes of vibrations of the tumbler in the two cases. In which case is the amplitude larger?  ?♂️Answer: The sound produced is louder when the tumbler is struck hard. The amplitude of vibration of the tumbler is larger when the glass is struck hard. Thus the loudness of sound depends upon the amplitude of vibration. |
1 Mark Questions and Answers
| Question 1. Choose the correct answer. Sound can travel through (a) Gases only |
| Question 2. Voice of which of the following is likely to have a minimum frequency? (a) Baby girl |
| Question 3. Identify the part which vibrates to produce sound in the following instruments. (a) Dholak (b) Sitar (c) Flute |
| Question 4. In the following statements, tick ‘T’ against those which are true and ‘F’ against those which are false. 1. Sound cannot travel in a vacuum. (T/F) |
| Question 5. Fill in the blanks with suitable words. 1. Loudness is determined by the ………….. of vibration. |
| Question 6. Define vibration. ?♂️Answer: Vibration is the to and fro or back and forth motion of an object. |
| Question 7. Which part of the human body is responsible for producing sound? ?♂️Answer: In humans, the sound is produced by the voice box or larynx. |
| Question 8. What is the length of vocal cords in men? ?♂️Answer: The vocal cords in men are about 20 mm long. |
| Question 9. Can sound travel in a vacuum? ?♂️Answer: No, sound cannot travel in a vacuum. |
| Question 10. What is meant by oscillatory motion? ?♂️Answer: The to and for the motion of an object is known as oscillatory motion. |
| Question 11. Define frequency. ?♂️Answer: The number of oscillations per second is called the frequency of oscillation. |
| Question 12. Define 1 hertz. ?♂️Answer: A frequency of 1 hertz means one oscillation per second. |
| Question 13. How is the frequency of a sound and pitch related? ?♂️Answer: If the frequency of vibration is higher then the sound has a higher pitch. |
| Question 14. Whose voice has a higher frequency – man or woman? ?♂️Answer: The voice of a woman has a higher frequency. |
| Question 15. What is a range of audible sounds? ?♂️Answer: Sound of frequency 20 Hz to 20,000 Hz is the audible range. |
| Question 16. Which animal can hear sounds of frequencies higher than 20,000 Hz? ?♂️Answer: Dogs can hear frequencies higher than 20,000 Hz. |
| Question 17. What is meant by base loudness level? ?♂️Answer: The base loudness level is defined as that loudness of sound that the human ear can just perceive. |
| Question 18. What is meant by noise pollution? ?♂️Answer: The presence of excessive or unwanted sound in the atmosphere is called noise pollution. |
| Question 19. If the frequency of a sound is below 20 Hz, will it be audible to human beings? ?♂️Answer: No, it will not be audible. |
| Question 20. In which state of matter does sound travel the 1. slowest 2. fastest? |
| Question 21. What happens to sound when it strikes a surface? ?♂️Answer: Sound gets reflected on striking a surface. |
| Question 22. Why do we hear the sound of the home of an approaching car before the car reaches us? ?♂️Answer: This happens because the speed of sound is much greater than the speed of the car. |
2 Mark Questions and Answers
| Question 1. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration? ?♂️Answer: Time taken for 500 vibrations = 1 second Time taken for 1 vibration = 1/500 second. ∴ Time period = 1/500 second. |
| Question 2. How do plants help in reducing noise pollution? ?♂️Answer: Plants absorb sound and so help us in minimizing noise pollution |
| Question 3. How can we control the sources of noise pollution? ?♂️Answer: We can control noise pollution by designing and installing silencing devices in machines. |
| Question 4. How can a hearing-impaired child communicate? ?♂️Answer: A hearing-impaired child can communicate effectively by using sign language. |
| Question 5. If the amplitude increases 3 times, by how much will the loudness increase? ?♂️Answer: If the amplitude increases three times, the loudness will increase by a factor of 9. |
| Question 6. The frequency of a given sound is 1.5 kHz. How many vibrations is it completing in one second? ?♂️Answer: Frequency = No.of vibrations/time ∴ No. of vibrations = Frequency x time = 1.5 x 1000 x 1 = 1500 vibrations |
| Question 7. Which characteristic of a vibrating body determines the loudness and pitch of the sound produced by it? ?♂️Answer: Amplitude. , Frequency. |
| Question 8. Why do we not hear echoes in our ordinary surroundings? ?♂️Answer: We do not hear echoes in our ordinary surroundings because the distance to hear an echo should be more than 17 m. |
| Question 9. We cannot hear the sound of the exploding meteors in the sky, though we can see them. Why? ?♂️Answer: Sound cannot travel through a vacuum. In space, there is a vacuum. Light can travel through a vacuum, so we can see the exploding meteor but cannot hear the explosion. |
| Question 10. We can hear the supersonic jet planes flying. How? ?♂️Answer: The supersonic jet planes fly in the air. Since sound can travel through the air, we can hear and then fly. |
| Question 11. What are vocal cords? What is their function? ?♂️Answer: The larynx has a pair of membranes known as vocal cords stretched across their length. The vocal cords vibrate and produce sound. |
| Question 12. When does a thud become music? ?♂️Answer: When thuds are repeated at regular intervals, it becomes music, e.g., the beating of drums or wood. |
| Question 13. How do birds and insects produce sound? ?♂️Answer: Birds chirp with the help of syrinx in their windpipe. Insects produce sound by flapping their wings. |
| Question 14. What is the function of the Eustachian tube in the human ear? ?♂️Answer: The vibrations of the spoken words reach our ears through the eustachian tube. |
| Question 15. (i) In our body which part of the ear receives sound waves? ?♂️Answer: Pinna helps in receiving sound waves.(ii) What may happen if the eardrum is absent from our ear? ?♂️Answer: If the eardrum is absent we would not be able to hear. |
| Question 16. Can a deaf or hard of hearing child speak? If not why? ?♂️Answer: A child having hearing impairment can not speak because if he is able to hear, he will leam to speak. |
| Question 17. Give an example each of: 1. Stringed instrument 2. Percussion instrument 3. Wind instrument 4. Striking instrument |
| Question 18. Can sound travel through water? How do whales communicate underwater? ?♂️Answer: Yes, sound can travel through water. Since sound can travel through water, the whales can communicate with each other. |
| Question 19. How is the pressure variation in a sound wave amplified in the human ear? ?♂️Answer: The pressure variation in a sound wave causes vibrations in the eardrum. These vibrations are amplified several times by the three bones. (The hammer, anvil and stirrup). |
| Question 20. How you can hear a friend talking in another room without seeing him? ?♂️Answer: Sound can travel in all directions and around comers. Light cannot travel around comers. Therefore, we can hear a friend talking in another room but cannot see him. |
3 Mark Questions and Answers
| Question 1. List sources of noise pollution in your surroundings. ?♂️Answer: The major sources of noise pollution are the sounds of vehicles, explosions, machines, and loudspeakers. |
| Question 2. What are the effects of noise pollution? ?♂️Answer: Due to noise pollution, a person may suffer from lack of sleep, hypertension and anxiety. If a person is exposed to noise continuously he may get temporary or permanent deafness. |
| Question 3. How can noise pollution be controlled in a residential area? ?♂️Answer:
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| Question 4. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency. ?♂️Answer: 40 vibrations in 4 seconds. 10 vibrations in 1 second Frequency =10 vibrations/sec. or 10 Hz. ∴ Time period = 1/10 sec. |
| Question 5. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer. ?♂️Answer: I would advise my parents to buy the house three lanes away from the roadside because there the noise from automobiles would be much less. |
| Question 6. What happens when we pluck the strings of a sitar? ?♂️Answer: When we pluck the strings of a sitar, the whole instrument vibrates and the sound is heard. |
| Question 7. Why is the voice of men, women and children different? ?♂️Answer: The voices of men, women and children are different because the length of vocal cords is different. The length of vocal cords is longest in men and shortest in children. |
| Question 8. How are we able to hear the sound? ?♂️Answer: The eardrum is like a stretched rubber sheet. Sound vibrations make the eardrum vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear. |
| Question 9. What sources in the home may lead to noise? ?♂️Answer: Television and transistor at high volumes, some kitchen appliances, desert coolers, air conditioners all contribute to noise pollution. |
| Question 10. What is the difference between noise and music? Can music become noise sometimes,? ?♂️Answer: Unpleasant sounds are called noise. Music is a sound which produces a pleasing sensation. If the music is too loud, it becomes noise. |
| Question 11. Draw a labelled diagram showing the structure of the human ear. ?♂️Answer:  |
| Question 12. What is the function of: 1. External ear. 2. Internal ear. |
| Question 13. Give some suggestions by which we can keep our ears healthy. ?♂️Answer:
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| Question 14. Can you hear the sound on the moon ? Explain. ?♂️Answer: We cannot hear the sound on the moon because sound requires a material medium to travel. On the moon there is no atmosphere and sound cannot travel in vacuum. |
| Question 15. What are ultrasounds ? How are they useful to us? ?♂️Answer: Sound having frequency higher than 20kHz is known as ultrasound, is used for
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5 Mark Questions and Answers
| Question 1. Sketch larynx and explain its function in your own words. ?♂️Answer: We produce sound in the larynx of our throats. The larynx has two vocal cords, which are folds of tissue with a slit like opening between them. When we speak, air passes through the opening and the vocal cords vibrate to produce sound. |
| Question 2. 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: The speed of light is more than the speed of sound. Therefore, even though thunder and lightning take place simultaneously, we see the lightning earlier. |
| Question 3. 1. What is SONAR? 2. What is the basic principle of its working ? 3. Explain its use. |
| Question 4. What is the use of ultrasound in medicine and industry ? ?♂️Answer: Use of ultrasound in medicine :
Use of ultrasound in industry :
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| Question 5. What is a sonogram ? Why is it preferred to X-rays ? ?♂️Answer: Sonogram is image of the internal organs. Ultrasound can pass through the human body and are reflected back. The reflections are recorded by computer and images are generated on the screen. Sonogram is not harmful and is therefore used for studying the foetus or stone or tumor in the organs. On the other hand, X-rays can be harmful if humans are exposed for longer time. |
| Question 6. 1. Name a property of sound which is (ii) different from that of light. 2. Why do some people have hearing impairment ? How do they communicate with others ? |
NCERT Solutions Class 8th Science All Chapter Question & Answer
- Chapter – 1 Crop Production and Management
- Chapter – 2 Microorganisms: Friend and Foe
- Chapter – 3 Synthetic Fibres and Plastics
- Chapter – 4 Materials: Metals and Non-Metals
- Chapter – 5 Coal and Petroleum
- Chapter – 6 Combustion and Flame
- Chapter – 7 Conservation of Plants and Animals
- Chapter – 8 Cell Structure and Functions
- Chapter – 9 Reproduction in Animals
- Chapter – 10 Reaching the Age of Adolescence
- Chapter – 11 Force and Pressure
- Chapter – 12 Friction
- Chapter – 13 Sound
- Chapter – 14 Chemical Effects of Electric Current
- Chapter – 15 Some Natural Phenomena
- Chapter – 16 Light
- Chapter – 17 Stars and the Solar System
- Chapter – 18 Pollution of Air and Water