CBSE Class 8 Science Sound VBQs

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

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

In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.

(a) Sound cannot travel in vacuum.
Answer : True

(b) The number of oscillations per second of a vibrating object is called its time period. 
Answer : False

(c) If the amplitude of vibration is large, sound is feeble. 
Answer : False

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. 
Answer : True

(e) The lower the frequency of vibration, the higher is the pitch. 
Answer : False

(f) Unwanted or unpleasant sound is termed as music.
Answer :

(g) Noise pollution may cause partial hearing impairment.
Answer : True

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) Shrillness of a sound is determined by the frequency of vibration

Question. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer : Number of oscillations in 4 seconds = 40
Number of oscillations in 1 seconds = 40/4 = 10
Therefore, frequency of pendulum = f = 10 Hz
Now Time period = 1/f = 1/10 = 0.1 sec.

Question. Explain in what way noise pollution is harmful to humans.
Answer : Noise pollution causes: (a) Lack of sleep, (b) Anxiety, (c) Hypertension.

Question. 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 : Number of vibrations in 1 seconds = 500
Therefore, frequency of vibration = f = 500 Hz
Now Time period = 1/f = 1/500 = 0.002 sec.

Question. Sketch larynx and explain its function in your own words.
Answer : The other name of larynx is voice box. It is present at the upper end of the windpipe. The function of larynx is to produce sound with the help of two vocal cords on passing air.

Question. List the sources of noise pollution in your surroundings.
Answer : Noise pollution sources are:
(a) Bus and car horns.
(b) Firecrackers and loudspeakers.
(c) High volumes in televisions and DJ etc.
(d) Sound of kitchen appliances.
(e) Sirens from factories

Question. 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 at roadside building.

Question. Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
Answer : (a) Dholak - Stretched membrane.
(b) Sitar - Stretched string.
(c) Flute - Air column.

Question. 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 : Speed of the light is much more than the speed of sound. Thus, lightning is seen earlier than thunder.

Question. What is the difference between noise and music? Can music become noise sometimes?
Answer : The type of sound which is unpleasant to listen is known as noise whereas music is a pleasant sound, which produces a sensation.
Yes, music can become noise when it’s too loud.