Question

A whistle S of frequency f revolves in circle of radius R at a constant speed v. What is ratio of largest and smallest frequency detected by a detector D at rest at distance 2R from the center of circle as shown in figure?

( take c as speed of sound)

• A. $(\frac{c+v}{c-v})$
• B. $\sqrt{2}(\frac{c+v}{c-v})$
• C. $\sqrt{2}$
• D. $\frac{(c+v)}{c\sqrt{2}}$

Answer 1

The correct option is A $(\frac{c+v}{c-v})$

Largest frequency $f_1$ and lowest frequency$f_2$
Largest frequency will be detected when the source approaches detector along the line joining and the smallest frequency will be detected when the source recedes the detector along the line joining them
$\frac{f_1}{f_2}=\frac{(\frac{c}{c-v})f}{(\frac{c}{c+v})f}=\frac{c+v}{c-v}$