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Ultrasonics
Human ear is sensitive to
sound frequencies between 20 Hz and 20,000 Hz.
Animals such as bats are able to hear frequencies above 20,000 Hz.
Frequencies above 20,000 Hz are called ultrasounds or ultrasonics.
Ultasounics
is used to locate underwater depths or are used for locating objects lying
deep on the ocean floor, etc. The technique is called sonar, short for sound
navigation and ranging.
The sound waves are sent
from a transmitter, and a receiver collects the reflected sound. The time
lapse is calculated. Along with the known sound velocity in water, the
distance of the object from the ocean surface can be estimated. The sonar
ranging is also used to ìseeî the shape and the size of the object.
3.
Differences
between sound waves and light waves
There
is a vast difference between the way sound waves travel and the way the
light waves travel. The most striking difference is that sound waves are
longitudinal waves, where as the light waves are transverse in nature. (In
addition to this, the light waves are emitted due to oscillating
electric and magnetic fields that are perpendicular to each other). Sound
waves need a material medium for transmission, whereas the light waves can
travel in vacuum also. Sound waves can propagate through any medium, solid,
liquid or gas; the light waves get scattered easily and hence may be able to
pass through certain transparent solids or on surface of liquids only. Sound
waves create pressure changes in the medium through which they are travelling
due to compression and rarefaction effects; light waves do not create
pressure changes in the medium in which they are travelling.
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The
Human Ear
Human ear is a
very intricate organ that has many purposes. Firstly it helps us
have a sensory perception of sound and secondly it helps us maintain
our balance.
The
human ear can be divided into three parts.
The external ear
consists of the physical ear and an air canal. The chief purpose of
this part is to collect sound waves and direct them to the middle
portion of the ear. The sound waves must get to the inner ear for us
to hear them. The sound waves enter the external ear, and are then
channeled down the external ear canal towards the tympanic membrane.
The membrane is stretched across the entrance to the middle ear and
vibrates when struck by sound waves. The tympanum is also known as
the eardrum.
The middle ear
consists of three small bones: malleus, incus, and stapes. The
middle ear also has an air cavity, which is connected to the throat
via a very small tube called Eustatian tube.
The function of the middle ear is to amplify the incoming
sound waves.
The
inner ear is a seashell-like spiral structure, called cochlea in
which the two chambers are separated by a thin diaphragm.
The diaphragm is called the basilar membrane. Acoustic
signals produce oscillations in this diaphragm. The organ of Corti
lies on top of the basilar membrane, and contains hair cells. The
outer hair cells mechanically amplify the vibration of the basilar
membrane, for the inner hair cells to do the "hearing".
The inner hair cells connect to the cochlear nerve. The central
nervous system receives all of these signals and processes them into
recognizable patterns. |
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