Question

How is it that we are able to hear sounds? Why are we able to hear different pitches of a particular frequency ( e.g., an ambulance approaches you then recedes from you)?

Answer 1

Sound waves are produced when the air is mechanically disturbed.Generally sound waves intensity are measured in the units of decibals.

The sound waves enters the ear canal and cause the eardrum to vibrate.These vibrations pass through three connected bones in the middle ear.This motion sets fluid moving in the inner ear.This moving fluid bends thousands od delicate hair like cells which converts the vibrations into "nerve impulses".

These nerve impulses are carried to the brain by the auditory nerve.In the brain the impulses ara converted into the vibrations we hear the sound.

The aubdible range of the human is 20Hz to 20,000Hz

The above case can be explained on the basis of DOPPLER EFFECT.According to this effect there is a relative change of the frequency,when ther is relative motion of the source of sound waves (ambulance) and observer(you).

As, the source of sound waves (ambulance) approaches to the observer the distance between source and the obsever is decreasing.Consequently,the siren sounds have the more frequency.As the pitch of sound waves of the siren is higher than the orniginal value because the sound waves reach you more frequently.So,the ear perceives the sound to be higher pitched as the sound waves reaches you

Hence the rate of frequency is increases in human ear