Question

A girl lying on a beach is awakened by her waterproof wrist alarm. She then swims about 50 yards off shore where she descends to the bottom with the alarm still ringing. Assuming the alarm is still vibrating at the same frequency, she will hear..

A. a higher frequency than on land

B. a lower frequency than in land

C. the same frequency

Answer 1

Option is C.

Sound is a longitudinal wave i.e., it propagates through the medium by successive compression and rarefaction.

Molecules in air are less packed than that in water. So velocity of sound in water is greater as it will require less time to compress and propagate between any two points.

But the for the same sound intensity, energy transferred through both the medium is same. As a result increase in velocity is compensated by the increase in wavelength thereby unchanging the frequency.