Question

When sound travels from air to water, the quantity that remains unchanged is,

• A. speed
• B. wavelength
• C. intensity
• D. frequency

Answer 1

The correct option is D

frequency

1. When sound travels from one medium to another, since there is a change in the medium, speed changes. Here the sound is traveling from rarer(air) to denser(water) medium,
2. According to the equation, $n=\frac{c}{v}$, where $n$ is the refractive index and $v$ is the velocity of light in the medium, the speed of sound decreases.
3. And we know that speed is directly proportional to wavelength i.e, $v=f\lambda$ and so wavelength also changes.
4. But frequency is a quantity that does not vary with the medium. Hence frequency remains constant.

Therefore, Option (D) is the correct answer.