Question

Two stationary sources each emit waves of
wavelength 2. An observer moves from one source
to another with velocity u. Then number of beats
heard by him
(1)2u/lambda
(2)u/lambda
(3)
(4)u/2lambda
​

Answer 1

Answer:

this is your answer

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Answer 2

Answer:

(2) u / λ

Explanation:

wave speed : v

source speed : vs = 0

original frequency : n

apparent frequency ( approach ) : n'

apparent frequency ( away ) : n"

observer speed : u

formula 1 v = nλ

hence....n = v/λ = v/2λ ( given that 2λ )

formula 2 : f' = f × ( v ± u ) / ( v ± vs )

hence....

n' = v/2λ ( v + u ) / ( v - 0 )

n" = v/2λ ( v - u ) / ( v - 0 )

now ...

beats = n' - n"

= [ v/2λ ( v + u ) / v ] - [ v/2λ ( v - u ) / v ]

= v/2λ ( 2u/v )

= u / λ