  Ncert solutions

Q 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 3:

• Sound cannot travel in a vacuum. (True)

Explanation: Sound needs a medium to travel.

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

Explanation: The number of oscillations per second is frequency. The time period is the time taken to complete one oscillation.

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

Explanation: Loudness is directly proportional to the square of the amplitude. If the amplitude is large then the sound will also be loud.

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

Explanation: Humans can hear the sound having a frequency range of 20 Hz to 20,000 Hz. The range sound with frequency below 20Hz is infrasound and range with frequency above 20,000 is ultrasound.

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

Explanation: Pitch is directly proportional to the frequency.

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

Explanation: Unwanted or unpleasant sound is noise.

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

Explanation: A lot of noise pollution can affect the eardrum which will result in hearing impairment.

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