Q 1. What does voice box or larynx of human produces?
Ans. Sound
Q 2. In which medium sound propagates the maximum?
Ans. Solid
Q 3. Name the sound producing organ in human.
Ans. Larynx
Q 4. What is vibration?
Ans. Back and forth motion of an object.
Q 5. Do all bodies produce sound?
Ans. No
Q 6.Name some of the musical instruments which are simply beaten or struck to produce music
Ans.Such instruments are manjira, ghatam, kartal, dholak, etc.
Q 7. Name a musical instrument which produces sound by blowing air into it.
Ans. Flute
Q 8. What is the unit of frequency?
Ans. Hertz
Q 9. What do you mean amplitude?
Ans. Vibrations produced by vibrating body in one second is known as amplitude.
Q 10. What is the maximum displacement of an oscillating object is called?
Ans. Amplitude
Q 11. How does sound help us?
Ans. Sound help us to communicate.
Q 12. What is the unit of loudness?
Ans. Decibel (dB)
Q 13. What is audible sound?
Ans. Frequency between 20 Hz to 20,000 Hz is audible sound.
Q 14. In which medium sound travels faster?
Ans. Solid
Q 15. A simple pendulum makes 20 oscillations in 40 seconds. What is the time period and frequency of its
Ans. Time period = Time No. of oscillation = 
= 2 sec.
Frequency = No. of oscillation Time = 
= 0.5 Hz
Q 16. Sonali heard sound of thunderbolt 5 second after she saw flash of lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s)
Ans. Distance of Sonali from the place of lightning = 330 × 5 = 1650 m
Q 17. What is frequency?
Ans. The number of oscillations per second is called frequency. Its unit is hertz.
Q 18. What do you mean by oscillatory motion?
Ans. The to and fro motion of an object is called vibration. This motion in both the direction from its mean position is called oscillatory motion.
Q 19. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
Ans. No, because in space there is no atmosphere and sound needs medium to travel.
Q 20. What do you mean by time period?
Ans. The time taken by a vibrating body to complete one oscillation is called the time period.
Q 21. What are the harms of noise pollution?
Ans. Lack of sleep, hypertension, anxiety and temporary or even permanent impairment of hearing.
Q 22. What do you mean by audible sound?
Ans. The sound which we can hear clearly is known as audible sound. It has a range of frequencies from 20 Hz to 20,000 Hz.
Q 23. What are infrasonic sounds?
Ans. Sounds which have frequency lower than 20 Hz are called infrasonic sounds.
Q 24. What is noise pollution?
Ans. The presence of unwanted and excessive sound in the environment is called noise pollution.
Q 25. State the differences between ultrasonic sound and infrasonic sound?
Ans.
| Ultrasonic sound | Infrasonic sound |
| (i) Sound of frequency higher than 20,000 Hz is called ultrasonic sound. | (i) Sound of frequency lower than 20 Hz is called the infrasonic sound. |
| (ii) Animals like dog, bat, monkey, deer, etc., can hear ultrasonic sound. | (ii) Animals like whale, elephant, hippopotamus, giraffe, etc., can hear infrasonic sound. |
Q 26. What are the methods to control noise pollution?
Ans. Following are the methods to control noise pollution:
- The noise pollution can be controlled by reducing the respective sources of noise pollution.
- The blowing of horns and speaker should be strictly avoided near schools and hospitals.
- More and more trees should be planted on roadside because trees absorb sound.
Q 27. What is the property of vibration which determines the pitch of the sound?
Ans. The frequency is the property which determines the shrillness or pitch of a sound. If the frequency of a sound is higher then we say that the sound has lower pitch.
Q 28. Define frequency.
Ans. The number of oscillations completed by a vibrating body in one second is called frequency. The unit of frequency is hertz. It is denoted by Hz. If a vibrating body makes 20 oscillations in a second we say that its frequency is 20 Hz. The human voice can produce frequency between 60 Hz and 13,000 Hz. It is interesting that a human ear can hear sound of frequency between 20 Hz to 20,000 Hz
Q 29. A string musical instrument was first plucked with a force of smaller magnitude and then with a force of greater magnitude. In which case would the instrument produce a louder sound?
Ans. The loudness of sound depends upon the amplitude of vibration. The amplitude of string is larger when it is plucked with greater force and hence the sound will be louder in that case.
Q 30. Differentiate between musical sound and noise.
Ans.
| Musical sound | Noise |
| (i) Musical sound is pleasant, smooth and agreeable to the ear. | (i) Noise is unpleasant, jarring and disagreeable to the ear. |
| (ii) It is produced by periodic vibrations which are regular and continuous. | (ii) It is produced by irregular vibrations which are discontinuous. |
| (iii) There are no sudden changes in loudness and pitch of musical sound. | (iii) There are sudden changes in loudness and pitch of noise. |
Q 31. How is sound produced and how is it transmitted and heard by us?
Ans. Sound is a form of energy produced and transmitted by a vibrating matter. It travels in form of waves through matter and moves in to and fro direction. When this wave reach eardrum it makes the eardrum to vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear the sound.
Q 32. Suppose a bell is ringing in a vacuum. Will you able to hear the sound?
Ans. We will not be able to hear the sound of vibration because sound cannot travel in vacuum.
Q 33. What is the function of hair and wax in ear canal?
Ans. The hair and wax in the ear canal help to keep out foreign debris such as dirt and bugs.
Q 34. When we speak and hear, does any part of our body vibrate? Name them.
Ans. Yes. When we speak, vocal cords vibrate to produce sound and when we hear, eardrum vibrate to receive the sound wave.
Q 35. We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us.
Ans. If the sound of vibrating body is audible then only we will be able to heard it otherwise we will not be able to hear it.
Q 36. Why we are able to hear sound of a clock clearer at night than in day?
Ans. The noise level is quite low at night. Therefore the sound of the clock appears much clearer at night than in the day.
Q 37. What are the uses of ultrasound?
Ans. Uses of ultrasound :
- The ultrasound or ultrasonic sound is used in investigating and tracking many medical problems.
- In industries, ultrasound is used for detecting Ëaws and cracks in metallic and other structures.
- Some operations, like bloodless surgery, can be done by applying this sound.
Q 38. Write a short note on the children having impaired hearing?
Ans. A child who has a moderately severe hearing loss and does not use a hearing aid will hear very little conversational speech, because speech develops as the direct result of hearing. A child with a moderately severe hearing loss may have defective speech, minimal expressive vocabulary and inadequate language structure. So, children with impaired hearing need special care. By learning sign language such children can communicate eÌectively.
Q 39. Prepare a list of famous Indian musicians and the instruments they play.
Ans.
(a) Ustad Amjad Ali Khan – Sarod
(b) Bismillah Khan – Sehnai
(c) Hariprasad Chaurasia – Flute
(d) Zakir Hussain – Tabla
(e) Ravi Shankar – Sitar
Q 40. Take a long thread. Place your hands over your ears and get some one to place this thread round your head and hands. Ask her to make the thread taut and hold its ends in one hand. Now ask her to draw her finger and thumb tightly along the thread (Fig. 13.13). Can you hear a rolling sound like that of a thunder? Now repeat the activity while another Mend stands near both of you. Can he hear any sound?
Ans. Yes.