Waves - Result Question 61

63. Two sound sources emitting sound each of wavelength λ are fixed at a given distance apart. A listener moves with a velocity u along the line joining the two sources. The number of beats heard by him per second is

[2000]

(a) u2λ

(b) 2uλ

(c) uλ

(d) u3λ

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Answer:

Correct Answer: 63. (b)

Solution:

  1. (b) Frequency received by listener from the rear source,

n=vuv×n=vuv×vλ=vuλ

Frequency received by listener from the front source,

n=v+uv×vλ=v+uλ

No. of beats =nn

=v+uλvuλ=v+uv+uλ=2uλ



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