NCERT Class VIII Science Solutions: Chapter 13-Sound Part 3

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SHORT ANSWER QUESTIONS

Question 16:

A simple pendulum makes . What is the time period and frequency of its oscillation?

Answer:

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?

Answer:

If the sound produced by a vibrating body is in the audible range, the sound produced will be heard by us otherwise we will not be able to hear the sound even though the body is vibrating.

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.

Answer:

The frying pan will vibrate. We will not be able to hear the sound of vibration because sound cannot travel in vacuum.

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.

Answer:

No, in space there is vacuum and sound cannot travel in vacuum.

Question 20:

List three sources of noise pollution in your locality.

Answer:

Vehicle noise, bursting of crackers, loudspeakers. (Any other reasonable sources of noise pollution should be accepted)

Image of source of noise pollution

Image of Source of Noise Pollution

Image of source of noise pollution

LONG ANSWER QUESTIONS

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?

Answer:

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

Image of compare the frequencies of sound with same loudness.

Image of Compare the Frequencies of Sound with Same Loudness.

Image of compare the frequencies of sound with same loudness.

Question 22:

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

Answer:

Hint: Explain how a vibrating body produces sound and how it travels through the air and is heard by us by our ears.

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