JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Waves & Sound

Two coherent sources of sound,

S_{1}

and

S_{2}

produce source waves of the same wavelength,

λ = 1 m

, in phase.

S_{1}

and

S_{2}

are placed 1.5 m apart (see fig). A listener located at L , directly in front of

S_{2}

finds that the intensity is at a minimum when he is 2 m away from

S_{2}

. The listener moves away from

S_{1}

, keeping his distance from

S_{2}

fixed. The adjacent maximum of intensity is observed when the listener is at a distance d from

S_{1}

. Then, d is:

Answer: (B)

Solution

Standing in front of

S_{2}

, the listener is

2

m from

S_{2}

and

2^{2} + 1. 5^{2} = 2.5

m from

S_{1}

, so the path difference is

0.5

= \frac{λ}{2}

, which is why the intensity is a minimum there. As he moves away from

S_{1}

while keeping his distance from

S_{2}

fixed at

2

m, the path difference grows, and the adjacent maximum appears when it reaches a full wavelength,

λ = 1

m. Then

S_{1} L - S_{2} L = 1

, so

d - 2 = 1

and

d = 3

JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Single correct option