Question

An obstacle is moving towards the source with velocity v. The sound is reflected from the obstacle. If c is the speed of sound and A. is the wavelength, then the wavelength of the reflected wave λ_r is

Options

• `lambda_"r" = (("c - v")/("c + v"))lambda`

• `lambda_"r" = (("c + v")/("c - v"))lambda`

• `lambda_"r" = (("c - v")/("c"))lambda`

• `lambda_"r" = (("c + v")/("c"))lambda`

Answer 1

`lambda_"r" = (("c - v")/("c + v"))lambda`

Explanation:

The frequency of reflected sound wave is

f_r = f`(("c + v")/("c - v"))`

∵ No change in velocity occurs due to reflection of sound wave.

Hence, `"c"/lambda_"r" = "c"/lambda (("c + v")/("c - v")) => 1/lambda_"r" = 1/lambda(("c + v")/("c - v"))`

`lambda_"r" = ("c - v")/("c + v")lambda`