A sound wave of frequency 100 Hz is travelling in air. The speed of sound in air is 350 m s-1. (a) By how much is the phase changed at a given point in 2.5 ms? (b) What is the phase difference at a given instant between two points separated by a distance of 10.0 cm along the direction of propagation?
Given:
Speed of sound in air 
Frequency of sound wave
(a) As we know,
⇒
Distance travelled by the particle:
Phase difference is given by:
On substituting the values, we get:
(b) For the second case:
Distance between the two points:
On substituting the respective values in the above equation, we get:
The phase difference between the two points is
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