- Books Name
- Class-8 Science Book
- PathSet Publications
- CBSE Class 8
SOUND NEEDS A MEDIUM TO PROPAGATE
- The traveling of sound is called the propagation of sound.
- Sound cannot propagate in the absence of a medium. The place where there is no air or air is removed is called vacuum.
- Sound does not propagate (travels) through a vacuum. It travels through solid, liquid and gas.
WE HEAR SOUND THROUGH OUR EAR
- The shape of the outer part of the ear is like a funnel.
- The tympanum is like a stretched membrane; which vibrates when sound waves strike it.
- Then the sound waves reach the eardrum or tympanum.
- The eardrum is like a stretched rubber sheet.
- From the eardrum, sound waves reach the inner ear; through the middle ear. From the inner ear, sound waves are sent to the brain.
How do we hear?
- We know that sounds are produced as waves in the air or any other medium.
- As these sound waves travel to our ears they convert them into electrical signals or messages that our brain can understand.
- Our ears have a special structure that allows this function.
- There are three major parts of the human ear:
- The outer ear (Pinna): It catches the sound waves and forwards them to the next part of the ear, that is, the middle ear.
- The middle ear: It converts the sound waves into vibrations that then travel to the inner ear. It can do this with the help of the eardrum. The eardrum is a thin rubber-like sheet present in the Middle ear. As the sound waves reach the eardrum, it vibrates and these vibrations propagate to the inner ear.
- The inner ear (cochlea): It receives the vibrations sent by the eardrum. It contains a liquid substance and the vibrations that enter the inner ear move through this liquid. There are tiny hairs present inside the inner ear that turn these vibrations into signals for the brain and pass them to the brain through the hearing nerve. As the brain receives the signal it interprets the sound. However, this whole process is so quick that we cannot notice it.