Ncert solutions science class 8 Solutions for Chapter 13 sound

Q 1) Choose the correct answer.

Sound can travel through

(a) gases only (b) solids only

(c) liquids only (d) solids, liquids and gases.

Choose the correct answer.

Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids and gases

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

Voice of which of the following is likely to have a minimum frequency?

(a) Baby girl

(b) Baby boy

(c) A man

(d) A woman

Q 2) Voice of which of the following is likely to have minimum frequency?

(a) Baby girl (b) Baby boy

(c) A man (d) A woman

Q 3) In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.

(a) Sound cannot travel in vacuum. (T/F)

(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)

(c) If the amplitude of vibration is large, sound is feeble. (T/F)

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)

(e) The lower the frequency of vibration, the higher is the pitch. (T/F)

(f) Unwanted or unpleasant sound is termed as music. (T/F)

(g) Noise pollution may cause partial hearing impairment. (T/F)

In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.

(a) Sound cannot travel in vacuum. (T/F)

(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)

(c) If the amplitude of vibration is large, sound is feeble. (T/F)

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)

(e) The lower the frequency of vibration, the higher is the pitch. (T/F)

(f) Unwanted or unpleasant sound is termed as music. (T/F)

(g) Noise pollution may cause partial hearing impairment. (T/F)

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

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.

Q 4) Fill in the blanks with suitable words.

(a) Time taken by an object to complete one oscillation is called __________.

(b) Loudness is determined by the __________ of vibration.

(c) The unit of frequency is __________.

(d) Unwanted sound is called __________ .

(e) Shrillness of a sound is determined by the __________ of vibration.

Fill in the blanks with suitable words.

(a) Time taken by an object to complete one oscillation is called __________.

(b) Loudness is determined by the __________ of vibration.

(c) The unit of frequency is __________

(d) Unwanted sound is called __________ .

(e) The shrillness of a sound is determined by the __________ of vibration.

Q 5) A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency

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?

Q 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?

Loudness of sound is measured in units of

(a) decibel (dB)

(b) Hertz (Hz)

(c) metre (m)

(d) metre/second (m/s)

Q 7) Identify the part which vibrates to produce sound in the following instruments.

    (a) Dholak (b) Sitar (c) Flute

Identify the part which vibrates to produce sound in the following instruments.

(a) Dholak

(b) Sitar

(c) Flute

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

What is the difference between noise and music? Can music become noise sometimes?

Q 8) What is the difference between noise and music? Can music become noise sometimes?

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

Q 9) List sources of noise pollution in your surroundings.

Pitch of sound is determined by its

(a) frequency

(b) amplitude

(c) speed

(d) loudness

List sources of noise pollution in your surroundings.

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

Explain in what way noise pollution is harmful to human.

Q 10) Explain in what way noise pollution is harmful to human.

Q 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.

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).

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.

Sketch larynx and explain its function in your own words.

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

Q 12) Sketch larynx and explain its function in your own words.

Q 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?

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 the reason for the delay in hearing the sound.

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?

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

Name two musical instruments which produce sound by vibrating strings?

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

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

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.

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

List three sources of noise pollution in your locality.

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?

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

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

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

Suggest three measures to limit noise pollution in your locality.