Compressions and Rarefactions - Teachoo.png

 

What is general meaning of word Compression?

It is a region of high pressure

Example

When a vibrating object moves forward in air as medium,

it pushes and compresses the air in front of it

creating a region of high pressure. This region is called a compression.

 

What is general meaning of word Rarefaction

It is a region of low pressure

Example

When a vibrating object moves backward in air as medium,

it creates a region of low pressure. This region is called a rarefaction.

 

Difference between Compression and Rarefaction

Compression Refraction
It is a region of high pressure It is a region of low pressure
Air particles are closely packed together Air particles are loosely packed

 

How does Sound Waves cause Compression and Rarefaction

We know that Sound waves travel through a medium like air

When an object vibrates, it moves in to and fro motion (forward and backward)

 

  1. When object moves in forward motion
    It causes nearby air particles to compress
    This creates a region of high pressure called compression

  2. When object moves back in backward motion
    It creates a region of low pressure
    This creates a region of low pressure called rarefaction

 

As the object vibrates (moves backward and forward), a series of compression's and rarefaction's is created in the air.

These make the sound waves propagate through the medium

Production of sound waves.png

 

particle and wave moment of a longitudanal wave

 

Questions

Intext Question 1 Page 163 - Explain how sound is produced by your school bell.

View Answer

 

NCERT Question 2 - Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.

View Answer

  1. Class 9
  2. Chapter 12 Class 9 - Sound

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.