When sound waves travel from air to water which one of the following remains constant?

• Time period

• Frequency

• Velocity

• Wavelength

B.

Frequency

Sound propagated in the form of longitudinal waves. When sound travels from one medium to another, both its velocity and wavelength undergo change. The velocity of sound in a given is obtained by equation 

          v = nλ

Where n - frequency of sound and λ is the wavelength of the medium. The velocity of sound is directly proportional to the wavelength.

The frequency of sound depends upon the source of the sound, not the medium of propagation. Hence, it does not change.