# NCERT Solutions for Class 8 Science Chapter 13 Sound

## Exercises

Question:- 1. Choose the correct answer.

Sound can travel through

(a) gases only              (b) solids only

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

Answer:- (d) solids, liquids and gases.

Question:- 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

Question:- 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)

1. True
2. False
3. False
4. True
5. False
6. False
7. True

Question:- 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.

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

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

(c) The unit of frequency is Hertz (Hz).

(d) Unwanted sound is called Noise.

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

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

Question:- 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?

Question:- 7. Identify the part which vibrates to produce sound in the following instruments.

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

Answer:- (a) Dholak :- Stretched membrane

(b) Sitar :- String of sitar

(c) Flute:- Air column

Question:- 8. What is the difference between noise and music? Can music become noise sometimes?

Answer:- Unpleasant sounds are called noise whereas sounds which are pleasant to hear are called Music. Yes, when the music is played at high volumes then sometimes it becomes noise.

Question:- 9. List sources of noise pollution in your surroundings.

Sources of noise pollution are

(a) Horns of vehicles.

(b) Bursting Firecrackers and loudspeakers.

(c) High volumes of televisions and transistors.

(d)  mixers, grinder and Juicer.

e) Sirens.

Question:- 10. Explain in what way noise pollution is harmful to human.

Answer:- A number of health issues like Stress, Headache, Hearing loss, Insomnia, Hypertension, and Anxiety are associated with noise pollution.