Question

A bat emits ultrasonic sound of frequency $100\text{kHz}$ in air. If the sound gets reflected (without transmission and loss of energy) from a water surface then wavelength of the reflected sound is
[speed of sound in air is $340{\text{ms}}^{-1}$]

• A. $0.55\times {10}^{-2}\text{m}$
• B. $0.34\times {10}^{-2}\text{m}$
• C. $0.65\times {10}^{-2}\text{m}$
• D. $0.74\times {10}^{-2}\text{m}$

Answer 1

The correct option is B $0.34\times {10}^{-2}\text{m}$

After reflecting from water surface, the sound wave will travel in air.
We know that velocity of sound wave is given by,
$v=\lambda f$, where $\lambda$ is wavelength and $f$ is frequency.
$\Rightarrow \lambda =\frac{v}{f}$
$\Rightarrow \lambda =\frac{340}{100\times {10}^3}=0.34\times {10}^{-2}\text{m}$