NCERT Question 2 - Chapter 12 Class 9 - Sound

Describe with the help of a diagram, how compression's and rarefaction's are produced in air near a source of sound.  

Answer

When an object vibrates, it forces the particles of medium around it to also vibrate

• As the object moves forward , it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression.
• As the object moves backward , it creates a region of low pressure. This region is called a rarefaction.
• As the object vibrates (moves backward and forward), a series of compression and rarefaction is created in the air. 

These make the sound waves propagate through the medium