Question

The frequency of sound waves in water is
(A) Same as that of frequency of source
(B) Less than frequency of source
(C) More than frequency of source
(D) Can’t say

Answer 1

Hint Sound needs a material medium to travel. It moves from one point to another through compression and rare-fraction. Assuming an ideal scenario, the energy of the sound wave wouldn’t reduce as it travels in different media. And energy is directly proportional to frequency.

Complete step by step answer
Sound needs a material medium to travel. It undergoes compression and rare-fraction. Compression is less than compared to rare-fraction. Interatomic forces are greater in water than air. When sound waves travel through water, pressure between the atoms increases. Waves experience less pressure when it travels through air.
While travelling in different media, waves change their properties like speed, wavelength etc. however ideally there is no change in the energy carried by the wave.
And energy is given as $E = h\nu = h\frac{c}{\lambda }$ where $h,\,\nu ,\,\lambda $ and c denote the Planck's constant, frequency, the wavelength and the speed of the wave
Now we see that if energy is constant it means that frequency is the same even if the medium changes.

Hence the correct option is A.

Note
One knows that the speed and color of the light wave are different in different media. Taking this as the basis of analogy, it is easy to get confused and develop a notion that the frequency changes. But one must note that
Colour is because of the wavelength of the light and not because of the frequency.
The wavelength changes along with the speed.