NCERT Solutions for Class 8 Science Chapter 13: Sound – Simplified Questions and Answers

NCERT Solutions for Class 8 Science Chapter 13: Sound

1. Choose the correct answer. Sound can travel through

Soln: (d) solids, liquids and gases

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

Soln: (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 a vacuum.	T
(b) The number of oscillations per second of a vibrating object is called its time period.	F
(c) If the amplitude of the vibration is large, the sound is feeble.	F
(d) For human ears, the audible range is 20 Hz to 20,000 Hz.	T
(e) The lower the frequency of vibration, the higher the pitch.	F
(f) Unwanted or unpleasant sound is termed as music.	F
(g) Noise pollution may cause partial hearing impairment.	T

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.
• (c) The unit of frequency is hertz.
• (d) Unwanted sound is called noise.
• (e) The shrillness of a sound is determined by the frequency of vibration.

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

• (a) Dholak: Stretched membrane (skin).
• (b) Sitar: Stretched strings.
• (c) Flute: Air column inside the hollow pipe.

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

Soln: Music is a pleasant sound produced by regular vibrations. Noise is an unpleasant or jarring sound caused by irregular vibrations. Yes, music can become noise if played at extremely high volumes.

9. List sources of noise pollution in your surroundings.

Soln: Common sources include vehicle horns, construction machinery, firecrackers, kitchen mixers, and high-volume loudspeakers.

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

Soln: It can cause various health issues like insomnia (lack of sleep), hypertension (high blood pressure), stress, and permanent hearing damage.

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.

Soln: I would suggest the house three lanes away. Since sound intensity decreases as distance from the source increases, this house will be quieter and offer a better environment than the one on the noisy main road.

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

Soln: The larynx (voice box) is at the top of the windpipe. It has two vocal cords stretched across a narrow slit. When air from the lungs is forced through this gap, the cords vibrate, producing sound.

Labels: Top view shows Vocal cord and Trachea. Side view shows Trachea.

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?

Soln: This happens because the speed of light is much faster than the speed of sound. Light reaches us almost instantly, while sound takes a few seconds to travel the same distance.