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) Choose the correct answer.
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.
- TV and radio’s sound.
- Sound of explosive.
10)Explain in what way noise pollution is harmful to human.
- Anxiety
- Permanent or temporary deafness.
- Hypertension
- Lack of sleep.
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.
Ans: – The road which is away from the roadside would have clam and pleasant situation as compared to the house which present near to the roadside which is noisy all the day. So, for better accommodation and peaceful life the house away from roadside is necessary.
12)Sketch larynx and explain its function in your own words.
Ans: – The sound is produced by the larynx or the voice box of our body. This larynx is made up with the two vocal cord as the sound passes through it produces the vibration as a result of that sound produces.
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?
Ans: – The lighting is seen earlier but the thunder is heard later. The main reason behind this is the speed of the light is more as compared to the sound. Generally we herd sound later but see the light first because of the speed difference. So, this light came to us faster as to the sound and we felt that.
