Question

The voice of a person who has inhaled helium sounds very high-pitched. Why?

Short answer

With helium, the speed of sound is high and hence the frequency. Therefore, the pitch of the wave becomes high.

Step-by-step solution

Write the concept of sound producing mechanism 

The sound-producing mechanism is based on resonating cavities, like the throat. The relatively fixed geometry of these cavities determines the relatively fixed wavelengths of sound. The expression for the frequency can be written as:

\(f = \frac{v}{\lambda }\)

Here, v is the speed of the wave and\(\lambda \)is wavelength of the sound wave.

Comparison of the speed of sound in helium and air

The speed of the sound wave depends on the gas-filled in cavities. The density of helium is much less than that of air; therefore, the sound's speed is three times as large as in the air. Thus, the person's frequency will go up by a factor of three, so the person sounds high-pitched.