NCERT Solutions class 8 Science 13. Sound Text Book Exercise

Exercise

1. Choose the correct answer :

Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids and air

Answer:

(d) solids, liquids and air

(a) Baby girl

(b) Baby boy

(c) A man

(d) A woman

Answer:

(c) A man

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)

Answer:

(a) T  (b) F  (c) F  (d) T  (e) F  (f) F  (g) T.

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.

Answer:

(a) Time period  (b) amplitude  (c) hertaz  (d) noise  (e) frequency.

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

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?

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

(a) Dholak 

(b) Sitar

(c) Flute

Answer:

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

Answer:

The unpleasant sound is called noise, wherease pleasant sound is called music. Noise can produce so many health hazard, whereas music brings about soothing affect.

Yes, music become noise when musical instrument produce high volume sound.

9. List sources of noise pollution in your surroundings.

Answer:

The sound of bus, truck, construction, T.V., radio and loudspeaker etc.

10. Explain in what way noise pollution is harmful to humans.

Answer:

(i) Lack of sleep, hypertention, anxiety etc are some of the problems that may be caused due to noise pollution

(ii) A person who is exposed to a loud sound continously, may get temporary or even permanent deafness.

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.

Answer:

I would suggest my parents to buy the house which is three lanes away from the roadside. This would protect us from noise pollution which is maximum on the roadside.

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