Page 29 - Physics_Form_4

Physics for Secondary Schools

The human ear
The human ear converts sound energy to mechanical energy and then to electrical
energy which acts as a signal sent to the brain via nerves. Human ears can discriminate
between sound based on frequency, amplitude and direction. The human ear consists of
three basic parts: the outer ear, the middle ear and the inner ear as shown in Figure 1.27.

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Outer ear Middle ear Inner ear
Temporal bone
Anvil Semicircular canals
Stirrup
Hammer Auditory nerves

Cochlea

Pinna Eardrum Eustachian tube
Ear canal

Figure 1.27: The human ear

The outer ear rarefaction allows the eardrum to move
The outer ear consists of the pinna and outward. In this way, the eardrum vibrates
the ear canal. The outer ear channels at the same frequency as an incoming
sound waves through the ear canal to the sound wave. The movements of the
eardrum of the middle ear. In the outer eardrum set the hammer, anvil and stirrup
ear, the sound is still in the form of a into motion. The three tiny bones amplify
pressure wave, with an alternating pattern the vibrations of the incoming sound
of high- and low-pressure regions. wave. Because the stirrup is connected to
the inner ear, the vibrations are transmitted
The middle ear to the fluid of the inner ear.

The middle ear is an air-filled cavity that The inner ear
consists of an eardrum and three small
interconnected bones, the hammer, anvil The inner ear consists of the cochlea, the
and stirrup. The Eustachian tube connects semicircular canals and the auditory nerve.
the middle ear to the throat. Its purpose is The cochlea and the semicircular canals are
to regulate pressure. filled with a water-like fluid. The fluid and
nerve cells of the semicircular canals help
A compression of the incoming sound in maintaining the body balance. The inner
wave forces the eardrum inward and a surface of the cochlea is lined with hair-like

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Student’s Book Form Four

Physics Form 4.indd 22 14/07/2025 14:42