Question

An ultrasonic source emits sound of frequency 220 kHz in air. If this sound meets a water surface, what is the wavelength of the reflected sound?

• A. $1.6\times {10}^{-3}m$
• B. $2.6\times {10}^{-3}m$
• C. $3.6\times {10}^{-3}m$
• D. $4.6\times {10}^{-3}m$

Answer 1

The correct option is A $1.6\times {10}^{-3}m$

Here, $v=220kHz=220\times {10}^3$
$=2.2\times {10}^{5}Hz$;
Speed of sound in air, $v_a=352m{s}^{-1}$
Speed of sound in water, $v_w=1.496m{s}^{-1}$
The reflected sound: After reflection, the ultrasonic sound continues to travel in air. If ${\lambda }_a$ is wave length in air, then
${\lambda }_a=\frac{v_a}{v}=\frac{352}{2.2\times {10}^5}=1.6\times {10}^{-3}m$