A driver is riding a car with velocity `v_c` between two vertical walls on a horizontal surface as shown in figure.A source of sound of frequency 'f' is situated on the car. (`v_c lt lt v`, where v is the speed of sound in air )

Consider the sound wave observed by the driver directly from car has a wavelength `lambda_1` and the sound wave after reflection from wall-1 observed by the driver has wavelength `lambda_2` then `(lambda_1-lambda_2)/(lambda_1+lambda_2)` is :

Options

A. `v_c/v`
B. `(2v_c)/v`
C. `v_c/(4v)`
D. `(4v_c)/v `

Explanation

`lambda_1=(v+v_c)/f , lambda_2=(v+v_c)/f`
`lambda_1-lambda_2=(2V_c)/f, lambda_1+lambda_2=(2v)/f`
`(lambda_1-lambda_2)/(lambda_1+lambda_2)=v_c/v`