NCERT Solutions for Class 8 Science Chapter 13 Sound

NCERT Solutions for Class 8 Science Chapter 13 Sound are written in detail by people who have expertise in the field and the entire chapter has been explained in a very simple yet in-depth manner. It is an excellent tool to enrich knowledge and make lessons for learners more exciting.

We help students to understand their fundamentals better, so that they can get a good score in any exam. Now, let’s move to the Chapter 13 CBSE Class 8 Science NCERT Solutions.

Chapter 13 Sound Class 8 Science NCERT Solutions

Exercise

1. Choose the correct answer. Sound can travel through
(a) Gases only
(b) Solids only
(c) Liquids only
(d) Solids, liquids and gases

Solution

(d) Solids, liquids and gases

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

Solution

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

Solution

(a) True
(b) False
(c) False
(d) True
(e) False
(f) False
(g) True

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.

Solution

(a) time period
(b) amplitude
(c) hertz
(d) noise
(e) frequency

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

Solution

Number of oscillations = 40
Total time = 4 seconds
Time taken to complete oscillation = 4/40 = 1/10 = 0.1 second
So, time period = 0.1 second
Frequency = 1/time period = 1/0.1 = 10 Hz.

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?

Solution

Total vibrations = 500
Time taken = 1 second
So, time period = 0.002 second
Time taken to complete one vibration 1/500 = 0.02 second

7. Identify the part which vibrates to produce sound in following instruments.
(a) Dholak
(b) Sitar
(c) Flute

Solution

(a) Stretched membrane
(b) Stretched strings
(c) Air column.

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

Solution

Noise	Music
(i) It is an unpleasant sound.	(i) It is a pleasant sound.
(ii) It causes discomfort.	(ii) It has a soothing effect.
(iii) It can lead to health problems.	(iii) It does not cause any such problem; rather it is good for health.

Yes, when loud music is played it become unpleasant to hear.

9. List sources of noise pollution in your surroundings.

Solution

Sources of noise pollution in our surroundings are loudspeakers, honking of horns, loud sounds of machines in factories, high volumes of T.V., radio, domestic appliances, etc.

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

Solution

Noise can be harmful in the following ways:
(i) High noise level can cause permanent hearing loss.
(ii) High noise can also cause headache and increase blood pressure.
(iii) It can cause health problems such as sleep, hypertension and anxiety, etc.

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.

Solution

My parents should buy the house, which is located three lanes away from the roadside because a roadside house has many disadvantages like lot of noise and smoke and dust produced by due to running vehicles.

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

Solution

Humans produce sound in the larynx, which is situated at the upper end of the windpipe. In order to produce sound, the larynx contains two vocal cords that are adjusted so that a slit-like opening is left between them. As we speak, air passes through these openings and the vocal cords vibrate.

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?

Solution

The speed of light is 3 × 10⁸ m/s, while that of sound is only 330 m/s. So, although lightning and thunder take place simultaneously in the sky and at the same distance from the Earth, lightening is seen first.