Question

An ultrasonic source emits sound of frequency $220kHz$ in air. If this sound meets a water surface, what is the wavelength of
(a) the reflected sound,
(b) the transmitted sound? (At the atmospheric temperature, speed of sound in air $=352m{s}^{-1}$ and in water $=1496m{s}^{-1}$)

Answer 1

Whenever a reflection takes place, the wavelength$\lambda$ remains unchanged. Hence the wavelength of reflected sound = wavelength of incident sound.

We know that $\lambda =\frac{speed\left(v\right)}{frequency\left(f\right)}=\frac{352}{220000}=1.6\times {10}^{-3}metres$

Whenever any wave enters a different medium, the frequency remains unchanged. Hence the wavelength of transmitted sound is given by

$\lambda =\frac{1496}{220000}=6.8\times {10}^{-3}metres$