Chapter 13 Sound

Question 1. A list of mediums is given below.

(i) wood

(ii) water

(iii) air

(iv) vacuum

In which of these mediums can sound travel?

(a) i & ii only

(b) i, ii & iii only

(c) iii & iv only

(d) ii, iii & iv only

Question 2. The loudness of sound depends on:

(a) its amplitude.

(b) its frequency.

(c) its time period.

(d) its speed.

Question 3. Which of the following statements are correct?

(i) Sound is produced by vibrations.

(ii) Sound requires a medium for propagation.

(iii) Light and sound both require a medium for propagation.

(iv) Sound travels slower than light.

(a) i & ii only

(b) i, ii & iii only

(c) ii, iii & iv only

(d) i, ii & iv only

Question 4. An object is vibrating at $50$ hertz. What is its time period?

(a) $0.02$ s

(b) $2$ s

(c) $0.2$ s

(d) $20.0$ s

Question 5. In order to reduce the loudness of a sound we have to

(a) decrease its frequency of vibration of the sound.

(b) increase its frequency of vibration of the sound.

(c) decrease its amplitude of vibration of the sound.

(d) increase its amplitude of vibration of the sound.

Question 6. Loudness of sound is measured in units of

(a) decibel (dB)

(b) hertz (Hz)

(c) metre (m)

(d) metre/second (m/s)

Question 7. The loudness of sound is determined by the

(a) amplitude of vibration

(b) ratio of amplitude and frequency of vibration

(c) frequency of vibration

(d) product of amplitude and frequency of vibration

Question 8. 1 hertz is equal to

(a) 1 vibration per minute

(b) 10 vibrations per minute

(c) 60 vibrations per minute

(d) 600 vibrations per minute

Question 9. Pitch of sound is determined by its

(a) frequency

(b) amplitude

(c) speed

(d) loudness

Question 10. Ultrasound has frequency of vibration

(a) between $20$ and $20,000$ Hz

(b) below $20$ Hz

(c) above $20,000$ Hz

(d) between $500$ and $10,000$ Hz

Question 11. Lightning can be seen the moment 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).

Question 12. Does any part of our body vibrate when we speak? Name the part.

Question 13. Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give reason for the delay in hearing the sound.

Question 14. When we hear a sound, does any part of our body vibrate? Name the part.

Question 15. Name two musical instruments which produce sound by vibrating strings?

Question 16. A simple pendulum makes $10$ oscillations in $20$ seconds. What is the time period and frequency of its oscillation?

Question 17. We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

Question 18. Suppose a stick is struck against a frying pan in vacuum. Will the frying pan vibrate? Will we be able to hear the sound? Explain.

Question 19. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.

Question 20. List three sources of noise pollution in your locality.

Question 21. 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?

Question 22. How is sound produced and how is it transmitted and heard by us?

Question 23. An alarm bell is kept inside a vessel as shown in Fig. 13.1. A person standing close to it can distinctly hear the sound of alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

Question 24. The townhall building is situated close to Boojho’s house. There is a clock on the top of the townhall building which rings the bell every hour. Boojho has noticed that the sound of the clock appears to be much clearer at night. Explain.

Question 25. Suggest three measures to limit noise pollution in your locality.