Question 1. Choose the correct answer.
Sound can travel through
(a)Gases only
(b)Solid only
(c)Liquid only
(d)Solids, liquids and gases
Solution : (d)air, liquid and solids
For the sound to travel it requires a medium. The medium can be solids, liquids and gases which provides the medium through which sound can travel.
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
Solution : (a) Baby girl.
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, 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 :
(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 ————–.
(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 taken by an object to complete one oscillation is calledtime period.
(b) Loudness is determined by the amplitude.
(c) The unit of frequency is hertz.
(d) Unwanted sound is called noise.
(e) Shrillness of a sound is determined by the pitch of vibration.
Question 5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Solution :
No. of oscillations = 40.
Time- taken = 4 sec.
Frequency = no. of oscillation/ time-taken
= 40/4 = 10 Hz.
Question 6. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per seconds. What is the time period of the vibration?
Solution :
No- of vibration in 1 second = 500.
Therefore, frequency= 500Hz.
Time-period = 1/ frequency
= 1/500 = 0.002 second.
Question 7. Identify the part which vibrates to produce sound in the following intruments.
(a) Dholak
(b) Sitar
(c) Flute
Solution :
(a) Dholak is a musical instrument. Sound in dholak is produced by the vibrations of stretched membrane.
(b) Sitar is a musical instrument. It consists of stretched strings. When a string is plucked, it sets into vibrations and produces sound.
(c) Flute is a hollow pipe. When air is pumped into it, the column of air inside the pipe is set into vibrations. As a result, a pleasant sound is produced.
Question 8. What is the difference between noise and music? Can music become noise sometimes?
Solution : The sound that is pleasing to the ears is called music. For example, the sound produced by violins, pianos, flutes, pungs, etc.
The sound that is unpleasing to the ears is called noise.
Some examples of noise are as follows:
(i) Sound produced by horns of buses and trucks.
(ii) Sound of electrical generators.
(iii) Sound of a gun shot.
(iv) Sound produced by jackhammers.
Yes. Music can become noise when played at high volumes.
Question 9. List sources of noise pollution in your surroundings.
Solution : Noise pollution sources are:
(a) Bus and car horns.
(b) Firecrackers and loudspeakers.
(c) High volumes in televisions and transistors.
(d) mixers at home
(e) Bursting of crackers, and sound of big machines in the factories.
Question 10. Explain in what way noise pollution is harmful to humans.
Solution : There are many harmful effects of noise pollution on humans like:
(i) Lack of sleep.
(ii) High blood pressure (Hypertension).
(iii) Temporary or permanent impairment of hearing.
(iv) Headache
(v) Stress
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 : I would suggest my parents to buy a house three lanes away from the roadside because there would be more noise along the roadside produced by the vehicles. And the amount of noise will decrease as one move away from the roadside.
larynx
Question 12. Sketch larynx and explain its function in your own words.
Solution : A sketch of larynx is shown below:
Larynx is that part of throat which is responsible for producing sound. Inside larynx, there are two vocal cords, which are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When we speak, air is forced into this small gap by the lungs which prompt vocal cords to vibrate. When the lungs force air through the slit, the vocal cords vibrate, producing sound.
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?
Solution : The speed of sound is 330 m/s while that of light is 3 x 108 m/s. Thus, speed of light is much higher than the speed of sound. This is the reason light reaches us before sound during a lightning.