# NCERT Solutions Class 8 Science Chapter 13 Sound

## NCERT Solutions Class 8 Science Chapter 13 Sound

NCERT Solutions Class 8 Science Chapter 13 Sound: National Council of Educational Research and Training Class 8 Science Chapter 13 Solutions – Sound. NCERT Solutions Class 8 Science Chapter 13 PDF Download.

### NCERT Solutions Class 8 Science Chapter 13: Overview

 Board NCERT Class 8 Subject Science Chapter 13 Chapter Name Sound Topic Exercise Solutions

### NCERT Solutions Class 8 Science Chapter 13 – Sound

CHAPTER: – 13

(SOUND)

Exercise: –

1) Sound can travel through

(a)gases only (b) solids only

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

Ans: – Option(d).

Explanation- (According to the principal of sound can travel through these three medium just speeds is different)

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.

Ans: –   Option(b).

Explanation- (As a baby boy produces sound low range)

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)

Ans: – True.

Explanation- (As sound always needs a medium for traveling)

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

Ans: – False.

Explanation- (This known as frequency)

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

Ans: – False.

Explanation- (It that case amplitude of vibration would be small)

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

Ans: – True.

Explanation- (As under 20Hz and above 20KHz human are not able to hear)

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

Ans: – False.

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

Ans: – False.

Explanation- (Music is a pleasant sound)

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

Ans: – True.

Explanation- (As the higher sound label or high frequency sound is bad for our health)

4) Fill in the blanks with suitable words.

(a) Time taken by an object to complete one oscillation is called___time period_______.

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

Explanation- (The more loudness the more amplitude of sound)

(c) The unit of frequency is ___Hertz_______.

(d) Unwanted sound is called __noise________ .

Explanation- (Unwanted sound is known as noise and pleasant sound is music)

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

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

Ans: –   As we know, time period= (total time/number of oscillation)

= (4/40) = 0.1S.

And frequency= (number of oscillation / total time)

=40/4 = 10Hz.

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?

Ans: –   As we know, time period= total time / numbers of oscillation.

Here, total time is 1 second, total number of vibrations is 500.

So, time period= 1/500 = 0.002S.

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

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

Ans: –   Dholak: – The stretched membrane of Dholak produced the sound.

Sitar: – The string present in the sitar produced the sound.

Flute: –   The air Column in the flute inside helps in producing of sounds.

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

Ans: –   There is common difference between the noise and music which is very well known to us as one is pleasant to us others not. The music is pleasant to us but the noise doesn’t give pleasure. As a result of the music is produce with the help of the pleasant sounds of different instrument. But is any music instrument produce heavy sounds then it will be noise as well.

9)List sources of noise pollution in your surroundings.

Ans: –   The source of sounds is

• Loud speakers.
• Vehicle sounds.
• Sound of explosive.

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

• Anxiety
• Permanent or temporary deafness.
• Hypertension
• Lack of sleep.