Question

A sound wave is produced in water and moves towards the surface of water and part of it moves in air. The velocity of sound in water is $1450\text{m/s}$ and that in air is $330\text{m/s}$. Which of the following statements is correct regarding the frequency $\left(f\right)$ and wavelength $\left(\lambda \right)$ of sound when it travels from water to air?

• A. $f$ and $\lambda$ will remain same.
• B. $f$ will remain the same but $\lambda$ will increase.
• C. $f$ will remain the same but $\lambda$ will decrease.
• D. $f$ will increase and $\lambda$ will decrease.

Answer 1

The correct option is C $f$ will remain the same but $\lambda$ will decrease.

Given that,
Velocity of sound in water, $v_w=1450\text{m/s}$
Velocity of sound in air, $v_a=330\text{m/s}$
Frequency depends on the source only. It does not depend on the medium of travel.
The velocity of the sound is given by
$v=f\lambda$
where $f$ is constant.
The velocity of sound decreases when it goes from water to air.
i.e $v_w<v_s$
So $\lambda$ will also decrease i.e ${\lambda }_w<{\lambda }_s$.