Define- compression and rarefaction.

Hint: Sound: Sound is a mechanical disturbance in the state of equilibrium that propagates through an elastic medium. Sound travels in the form of waves. Sound is a longitudinal wave. There are three types of sound waves- longitudinal wave, mechanical wave, pressure wave. They can travel through air, water and solid in the form of vibrations.

Complete step by step solution:
Sound wave thus consists of alternating compression and rarefaction or region of high pressure or region of low pressure. The properties of sound waves are: wavelength, amplitude, frequency, time period, and velocity.
Now here we talk about compression and rarefaction. When particles of sound waves are closer to each other is known as Compression. When particles of sound waves are away from each other this phenomena is called rarefaction.
When sound waves travel in air, the particles of air come closer to each other is known as compression and when particles are away from each other is known as rarefaction.
When the compression takes place in the medium, the density and pressure of the medium is increased. When refraction takes place in the medium, the density and pressure of the medium is decreased. The increase and decrease of pressure and density is temporary.
Compression is called the region of high pressure and density where rarefaction is the region of low pressure and low density. Here we illustrate the phenomena of compression and rarefaction by the image of tong, when we strike the tong the sound wave produces and compression and rarefaction takes place.

Note: Sound frequency between 20Hz to 20000Hz is known as audible frequency. Frequency less than 20Hz is known as infrasound and more than 20000Hz is known as ultrasound. There are many factors in which sounds are dependent are pitch, amplitude, frequency, source. The unpleasant sound is also known as “noise”.