How humans hear sound - class-VIII

If pitch is high frequency is high and vice versa.

Our inner ear is shaped like a snail and is called cochlea.

Combination of notes that produced jarring effect on the ear is called discord. Discord is lack of harmony between notes sounding together.

The sensation of hearing of any sound persists in our brain is 0.1 s. This is called the persistence of hearing. The persistence of hearing of human beings is not more than $\frac{1}{5},s$

The sound waves produces vibration of the ear drum and subsequently a forceful vibration of the bones of the middle ear. This high amplitude vibration is transmitted to the fluid of the inner ear and encoded in the nerve signal which is sent to the brain.

In order for us to be able to hear a sound at all, it has to be above a certain level. This level is called the auditory threshold or hearing threshold. Humans have a hearing threshold of around $0$ decibels. Above this threshold, sounds with higher sound pressure levels are heard as louder noises. Sounds above $90, dB$ can lead to chronic hearing damage if people are exposed to them every day or all the time. Hearing becomes uncomfortable if the sound pressure level is above $110$ decibels (threshold of discomfort), and it becomes painful above $130$ decibels (threshold of pain).

Sound from the outside world are collected by pinna and reach the inner ear through auditory canal.

When the sound waves strike the eardrum or tympanic membrane it starts vibrating. Sound from the outside world are collected by pinna and reach the eardrum through auditory canal.

The tympanum of the ear receive the sound in the form of compressions and rarefaction. These compressions and rarefaction strike the ear drum, the ear from begins to vibrate.

Time taken by 2 consecutive compression or rarefaction is called the time period of the wave.
Sound of a voilin and a flute is different due to their different pitches.

Never insert any pointed object into the ear. It can damage the eardrum and make a person deaf. Ears are very fragile and delicate organs.

The compressions and rarefactions are transmitted across the middle ear through the three ear ossicles. The vibrations produced in the ear drum are amplified.

Cochlea is a coiled and fluid filled tube having sense of hearing. The movement of the fluid in the cochlea due to the vibrations stimulates the auditory nerve .

When sound strikes the ear drum, it vibrates and this vibration is carried to the inner ear from where it is carried to the brain in the form of impulse. The brain then gives the signal and we hear the sound.

The compressions and rarefactions are transmitted across the middle ear through the three ear ossicles. The vibrations produced in the ear drum are amplified.

The tympanum of the ear receive the sound in the form of compressions and rarefaction. These compressions and rarefaction strike the ear drum, the ear from begins to vibrate.

Cochlea is a coiled and fluid filled tube having sense of hearing.the movement of the fluid in the cochlea due to the vibrations stimulates the auditory nerve.

Eardrum is the thin stretched membrane at the end of inner ear , which vibrates when sound wave strikes it .

Ear canal is provides the path to sound to ear .

Sound waves or vibrations enter the inner ear through middle ear bones or ossicles.

Cotton, put inside ear, damps  the vibration entering the ear. So, when the damped sound reaches the eardrum, its vibration becomes lower than original. So, we find it difficult to hear.

A very loud sound damages the hair cells of the inner ear. The hair cells die and stop sending sound signals to the brain. Once damaged, these hair cells do not grow back.

65 dB loudness causes no harm to human ears. But the damage occurs if the loudness exceeds 65 dB.

Pitch is known as the response of human ear to sound in terms of its shrillness.

Bats produce ultrasonic sound and thus humans cannot hear them. Bats emit sound in the range of $20,000$ to $100,000\ Hz$ which is beyond our audible range.

When outer or middle ear gets damage causing insufficient transfer of sound to inner ear.

All of the options are correct.

A normal human ear possess nearly 25000 hair cells.

It is a false statement. It is possible to have a mixed hearing loss.

Muscles around middle ear contracts while yawning. So, we are not able to hear while yawning.

When an object vibrates, it vibrates the neighbouring particles of the medium. These vibrating particles then vibrate to the adjacent particles. Vibrations in an object create disturbance in the medium and consequently compressions and rarefactions.  In this way, vibrations produced by an object are transferred from one particle to another in the form of compressions and rarefactions till it reaches our ear.
Region of high pressure and high density is called compression and region of low pressure and low density in the air is called rarefaction. As the object continues to vibrate, it produces a series of successive compression and rarefaction in the air, thus, propagating sound through the air and finally reaches our ears.

The sensation of hearing of any sound persists in our brain for 0.1s.This is called the persistence of hearing.

To hear an echo, sound must travel to the obstacle and back. The minimum time for human ear persistence is 0.1 seconds. Distance = (speed * time) / 2 = (330 * 0.1) / 2 = 16.5 meters. 17.5 meters is the closest provided option.

Given :   Area of stirrup        $A _s = 3.2 mm^2     = 3.2\times 10^{-6}$ $m^2$