Ultrasound

A graph charting increasing sound frequencies. The range of human hearing is between 20 hertz (low pitch) and 20 kilohertz (high pitch). Frequencies above 20 kilohertz are classed as ultrasound.

Ultrasound waves are sound waves which have a frequency higher than the upper limit for human hearing - above 20,000 Hz.

Ultrasound waves are longitudinal because they are simply high frequency sound waves i.e. above 20 kHz.

Different species of animal have different hearing ranges.

This explains why a dog can hear the ultrasound produced by a dog whistle, but humans cannot.

Question

A builder uses an ultrasonic device to measure the length of a room.

The device shows that the distance from one wall to the opposite wall is 8.25 m.

If the speed of ultrasound in air is 330 m/s, how long does it take for the ultrasound to travel to the far wall and back again?

Speed = \frac{\text{distance}}{\text{time}}

Time = \frac{\text{distance}}{\text{speed}}

Distance to opposite wall = 8.25 m

Speed of sound = 330 m/s

Time taken from device to opposite wall = \frac{\text{8.25 m}}{\text{330 m/s}}

Time taken from device to opposite wall = 0.025 s

Time taken from device to opposite wall and back again:

= 0.025 s x 2 = 0.050 s

The time taken for the ultrasound to travel to the far wall and back again is 0.050 s.