Question

A bat emitting an ultrasonic wave of frequency $4.5\times {10}^{4}Hz$ at speed of $6m/s$ between two parallel walls. The two frequencies heared by the bat will be

• A. $4.67\times {10}^{4}Hz$, $4.34\times {10}^{5}Hz$
• B. $4.34\times {10}^{4}Hz$, $4.67\times {10}^{4}Hz$
• C. $4.5\times {10}^{4}Hz$, $5.4\times {10}^{4}Hz$
• D. $4.67\times {10}^{3}Hz$, $4.34\times {10}^{4}Hz$

Answer 1

The correct option is B $4.34\times {10}^{4}Hz$, $4.67\times {10}^{4}Hz$

Frequency received by bat after reflection from wall (1),
$f_1=f\left[\frac{v+u}{v-u}\right]$
$=4.5\times {10}^4\left[\frac{330+6}{330-6}\right]$ [given $t=4.5\times {10}^{4}Hz$]
$=4.67\times {10}^{4}Hz$
Frequency received by bat after reflection from wall (2),
$f_2=f\left[\frac{v-u}{v+u}\right]$
$=4.5\times {10}^4\left[\frac{330-6}{330+6}\right]$
$=4.34\times {10}^{4}Hz$