RBSE Solutions for Class 8 Science Chapter 13 Sound

Rajasthan Board RBSE Solutions for Class 8 Science Chapter 13 Sound Textbook Exercise Questions and Answers.

RBSE Class 8 Science Solutions Chapter 13 Sound

RBSE Class 8 Science Sound InText Questions and Answers

Page 160

Question 1. 
When we speak, does any part of our body vibrate?
Answer:
Yes, when we speak the vocal cords inside our throat ‘vibrates.

Page 165

Question 2. 
I wonder why my voice is different from that of my teacher!
Answer:
Children have shorter vocal chords as compared to adults due to which the vibration is large or frequency is high and they produce  shrill sound.

RBSE Class 8 Science Sound Textbook Questions and Answers

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
Answer:
(c) A man.

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 is, 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

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

Question 5. 
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
Frequency = \(\frac{\text { No. of oscillations }}{\operatorname{Time}(\mathrm{s})}=\frac{40}{4}\)
= 10 Hz 
Time Period = \(\frac{1}{\text { Frequency }}=\frac{1}{10}\) = 0.1 sec.
 
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? 
Answer:
Frequency = 500 Hz 
Time Period = T = ?
Time Period =\(\frac{1}{\text { Frequency }}=\frac{1}{500} \)= 0.002 sec.

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

Question 8. 
What is the difference between noise and music? Can music becomes noise sometimes?
Answer:

Yes, if the intensity of music becomes very high, then music also appears to be noise.

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

1. Sounds of vehicles 
2. Loudspeaker 
3. Machines 
4. Firecrackers 
5. Radio and Television 
6. Few devices in the kitchen 
7. Cooler 
8. Air Conditioner 
9. Washing Machine 
10. Vacuum Cleaner 
11. Telephone 
12. Typewriter 
13. Vendors 
14. Rallies 
15. Festivals 
16. Social Programmes like Marriages 
17. Relegious programmes 
18. Aeroplanes takings off at the airport.

Question 10. 
Explain in what way noise pollution is harmful to humans. 
Answer:
Noise pollution is harmful to humans in the following ways:

1. Noise pollution causes lack of sleep.
2. It can cause high blood pressure.
3. The capacity to hear can be temporarily or permanently reduced.
4. It can cause tension like problems in brain. 

Question 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:
We would suggest our parents to buy a house three lanes away from roadside. The reasons are:

1. Excessive noise due to vehicles on road.
2. The continuous smoke emitted from vehicles causes air pollution.
3. Excessive noise pollution occurs during traffic jams.

Question 12. 
Sketch larynx and explain its function in your own words.
Answer:
The two vocal cords are stretched on both sides of larynx in such a way that there is a small slit between them for the passage of air. When the lungs force air, through the slit, the vocal cords vibrate, producing sound. When the vocal cords are tight and thin, the type or quality of voice is different from when they are loose and thick.

Question 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?
Answer:
This happens due to the difference between their velocities. Speed of light is much larger than speed of sound. Therefore light reaches us before sound. And thus, lightning and thunder take place in sky at the same time and at the same distance from us but lightning is seen earlier and thunder is heard later.