## Ultrasound

**Ultrasound or ultrasonic waves are sound waves with frequencies above 20,000 Hz. These waves are undetectable by humans as they lie above the audible range.**

Ultrasonic waves have high frequencies and short wavelengths.

We know that **the velocity of sound waves in air is 330 m/s**. Therefore for an audible sound with frequency 1000 Hz we can calculate the wavelength using the wave equation:

velocity = wavelength x frequency

*Rearranging equation,*

wavelength = velocity/frequency

wavelength = 330/1000

wavelength = 0.33m

However, if the sound is in the ultrasonic range for example 100,000 Hz then the wavelength can be calculated as:

wavelength = 330/100000

wavelength = 0.0033 m = 0.33 cm

Hence the ultrasonic wave with is shorter wavelength can be transmitted as a beam and undergoes little diffraction; these properties of ultrasound are put to use in various applications.