(a) What is ultrasound? What is the difference between ordinary sound and ultrasound?
(b) Write any three applications (or uses) of ultrasound.

(a). Ultrasound waves: The sounds having frequencies above $20000\ Hz$ are ultrasound waves. A human ear can't be able to hear ultrasound waves.

Difference between ordinary sound and ultrasound:

Ordinary Sound	Ultrasound
The ordinary sound has a frequency between $20\ Hz-20,000\ Hz$.	Ultrasound has a frequency above $20000\ Hz$
An ordinary sound is audible to the human ear.	An ultrasound is not audible to the human ear.

(b). Application of ultrasound:

1. In the Medical field ultrasound is used to examine the internal body organs.

2. In Industry ultrasound is used to detect the faults in the metal.

3. Ultrasound is used to find cracks in a structure.