Lesson: Sound

Choose the correct answer.

Sound can travel through
(a) gases only 

(b) solids only
(c) liquids only 

(d) solids, liquids and gases.

d

Which of the following voices is likely to have minimum frequency?
(a) Baby girl 

(b) Baby boy
(c) A man 

(d) A woman

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. (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)

(a) True

(b) False

(c) False

(d) True

(e) False

(f) False

(g) True

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.

(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 (Hz).
(d) Unwanted sound is called noise.
(e) Shrillness of a sound is determined by the frequency of vibration.

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

Frequency of oscillation is the number of oscillations of a vibrating object per second.

Therefore, here the frequency is 40 vibrations /4 seconds = 10 Hertz.

Time period is the time required to complete one oscillation. Therefore, it is the inverse of the time period. Therefore, here the time period = 1/10 = 0.1 second.

 

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?

Time period is the inverse of the frequency.
Time Period = 1/Frequency of oscillation = 1/500 = 0.002 sec.

 Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak

(b) Sitar

(c) Flute

(a) Diaphragm (stretched membrane)
(b) String
(c) Air column

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

Noise is unwanted sound that is unpleasant to the human ear, whereas music is a pleasant sound.
Music can become noise. When someone tries to enjoy very loud music, it can become noise for someone else. When loud music is played during celebrations, it can be annoying for many people.

List sources of noise pollution in your surroundings.

Some sources of noise pollution are as follows:

·         Televisions played at high volumes and sound of generators running.

·         Bursting of crackers and blaring sound from loudspeakers.

·         Honking horns of vehicles.

·         Home appliances such as mixers, desert coolers, etc.

Explain in what way noise pollution is harmful to humans.

Noise pollution is harmful to humans and can lead to a number of health issues. Some examples are given below:

1.      Loss of hearing

2.      Hypertension

3.      Insomnia

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.

A house by the roadside will have more noise pollution produced from transportation vehicles plying on the road. On the other hand, a house which is three lanes away from the roadside would be quieter. Therefore, I would suggest to take the house that is away from the roadside.

Sketch larynx and explain its function in your own words.

Larynx is a part of the throat and it is responsible for production of sound.

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?

During lightning, we see the streak of light earlier than hearing the sound of thunder because the speed of light is greater than the speed of sound. Owing to this, the light from a lightning reaches us faster than the sound of thunder.