Question 1. Choose the correct answer.
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids, and gases
Solution 1.
(d) solids, liquids, and gases
Question 2. Voice of which of the following is likely to have a minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Solution 2.
(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 a vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called it’s period. (T/F)
(c) If the amplitude of the vibration is large, the 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)
Solution 3.
a) Sound cannot travel in a vacuum. True
b) The number of oscillations per second of a vibrating object is called it’s period. False
c) If the amplitude of the vibration is large, the sound is feeble. False
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. False
f) Unwanted or unpleasant sound is termed as music. False
g) Noise pollution may cause partial hearing impairment. 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) The shrillness of a sound is determined by the __________ of vibration.
Solution 4.
(a) Time taken by an object to complete one oscillation is called a 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.
Question 5. A pendulum oscillates 40 times in 4 seconds. Find its period and frequency
Solution 5.
The number of oscillations per second of the vibrating body is known as the frequency of oscillation.
Frequency = Total number of oscillations
Total time taken
= 50/5
= 10 Hz
The period is the time taken to complete one oscillation. It is also the inverse of frequency.
Period = 1/ Oscillating frequency
= 1/10
= 0.1 s
∴ frequency = 10 Hz
Time period = 0.1 s
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 period of the vibration?
Solution 6.
The period is defined as the time taken to complete one oscillation. It is also the inverse of frequency.
Period = 1
Oscillation frequency
Oscillation frequency = 500 Hz
Time period = 1/500 = 0.002 s
Question 7. Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
Solution 7.
| Musical instrument | Vibrating part |
| Dholak | Stretched membrane |
| Sitar | Stretched string |
| flute | Air- column |
Question 8. What is the difference between noise and music? Can music become noise sometimes?
Solution 8. A pleasant sound is called music.
For example flutes, pianos, and violins are pleasant to our ears.
An unpleasant sound is called noise.
Sounds that are unpleasant to hear are:
(a)Sounds from bus horns and truck horns.
(b)Electrical generator sounds.
(c)Gunshot sounds.
(d) sound from home appliances
Yes, sometimes high-volume music can become noise too.
Question 9. List sources of noise pollution in your surroundings.
Solution 9. Following are some sources of noise pollution:
(a) Bus and car horns.
(b) Firecrackers and loudspeakers.
(c) High volumes in televisions and transistors.
(d) mixers at home
e) Sirens from factories
Question 10. Explain in what way noise pollution is harmful to humans.
Solution 10. Noise pollution causes a number of health problems like:
(a) Stress
(b) Headache
(c) Hearing loss
(d) Insomnia
(e) Hypertension
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.
Solution 11. I would suggest my parents buy a house that is three lanes away from the roadside because the level of noise pollution will be less there. On the other hand, the level of noise pollution will be very high near the house on the roadside because of the vehicles.
Question 12. Sketch the larynx and explain its function in your own words.
Solution 12.
The larynx moves, when we swallow something. Inside the larynx, there are two vocal cords. The air passes through the windpipe between the two vocal cords. Sound is produced when the lungs force the air into the gap when we speak and this vibrates the vocal cord.
Question 13. Lightning and thunder take place in the sky at the same time and the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Solution 13. Lightning is seen earlier and thunder is heard later because the Speed of the light is more than the speed of sound.