Write answers to the following questions .

(a) How is sound produced ?

(b) What does the intensity of sound depend upon ?

(c) Explain how the frequency of oscillation is related to the length of a pendulum and the amplitude of its oscillation.

(d) Explain the two ways by which the pitch of the sound generated by a stretched string can be changed.

(a) The back and forth movement of an object produces sound. An object moving back and forth is said to be in vibration. Hence, sound is produced by vibrating objects.

(b) Intensity of sound depends on the amplitude of vibration of the sound. It is proportional to the square of amplitude of vibration of the sound.

(c) Frequency of oscillation of a pendulum decreases with increase in the length of the pendulum and vice-versa. It is independent of the amplitude of oscillation of pendulum provided the amplitude is small.

(d) Frequency or pitch of vibration of a stretched string can be changed by varying the

• tension in the string: If the string of the instrument is under high tension, then the pitch of the note produced on plucking the string will be high i.e. the note will be shriller because frequency of vibration of the string will be high.
• thickness of the string: If the string of the instrument is thin, then the pitch of the note produced on plucking the string will be high as frequency of vibration of the string will be high.