A sound wave of frequency f travels horizontally to the right. It is reflected from a large vertical plane surface moving to the left with a speed v. The speed of sound in the medium is c, then study following statements(i) The frequency of the reflected wave is f(c+v)c−v(ii) The wavelength of the reflected wave is c(c−v)f(c+v)(iii) The number of waves striking the surface per second is f(c+v)c(iv) The number of beats heard by a stationary listener to the left of the reflecting surface is fvc−vCorrect statements are
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a
(i),(ii) and (iii)
b
(i),(ii) and (iv)
c
(ii),(iii) and (iv)
d
(i),(iii) and (iv)
answer is A.
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Detailed Solution
Number of waves striking the surface per second (or the frequency of the waves reaching surface of the moving target) n′=(c+v)λ=f(c+v)cNow these waves are reflected by the moving target(Which now act as a source). Therefore apparent frequency of reflected second n′′=cc−vn′=fc+vc−vThe wavelength of reflected wave =cn′′=c(c−v)f(c+v)The number of beats heard by stationary listener=n′′−f=fc+vc−v−f=2fv(c−v)Hence option (a) is correct.