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)
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When object moves in forward motion
It causes nearby air particles to compress
This creates a region of high pressure called compression
-
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
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Questions
Intext Question 1 Page 163 - Explain how sound is produced by your school bell.
NCERT Question 2 -
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
