WAVES
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| WAVES |
A wave is a form of
disturbance which travels through a material medium due to the repeated
periodic motion of the particles of the medium about their mean position.A
sudden and short duration disturbance is called a pulse.Waves are broadly of
two types.
i. Mechanical wave
ii.Electromagnetic wave
MECHANICAL WAVE
The wave which require
material medium (solid,liquid,gas) for their propagation are called mechanical
waves elastic wave Mechanical wave are of two types.
i. Transverse waves
ii.Longitudinal waves
TRANSVERSE WAVES
In these
waves,displacement of the particles of the medium is at right angles to the
direction of propagation of the waves.These waves can be polarized and can
travel in solids and liquids only.
These waves travel in
the form of crests and troughs.
LONGITUDINAL WAVES
In these waves,
displacement of the particles of the medium is in the direction of propagation
of the waves.
These waves cannot be
polarized and can travel in solids,liquids and gases.
ELECTROMAGNETIC WAVES
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| ELECTROMAGNETIC WAVES |
The waves which do not
require medium for their propagation i.e., which can propagate even through the
vacuum are called electromagnetic waves.
Cathode rays, canal
rays, ɑ rays,𝛃 rays sound waves and
ultrasonic waves are not electromagnetic waves.
Some Important Electromagnetic Waves
ELECTROMAGNETIC
WAVES
|
DISCOVERER
|
WAVELENGTH
RANGE
|
FREQUENCY
RANGE
|
𝜸-rays
|
Henry
Becqueral
|
10-14 to
10-10
|
1020 to
1018
|
X-rays
|
W.Rontgen
|
10-10 to
10-8
|
1018 to
1016
|
Ultraviolet
rays
|
Ritter
|
10-8 to
10-7
|
1016 to
1014
|
Visible
radiation
|
Newton
|
3.9*10-7 to
7.8*10-7
|
1014 to
1012
|
Infra-red
rays
|
Hershel
|
7.8*10-7 to
7.8*10-3
|
1012 to
1010
|
Short
radio waves or Hertz hertzian waves
|
Heinrich
|
10-3 to
1
|
1010 to
108
|
Long
radio waves
|
Marcony
|
1
to 104
|
108 to
106
|
SOUND WAVE
Sound is a form of
energy which produces the sensating of hearing.
Sound waves are
longitudinal mechanical waves.
Sound waves have low
frequency and high wavelength.
Sound waves cannot
travel in vacuum.
The rebouncing back of
sound when it strikes a hard surface is called reflection of sound.
The repetition of sound
due to reflection of sound wave is called an echo.
According to their
frequency range, longitudinal mechanical waves are divided into the following
categories
- Audible or sound waves The
longitudinal mechanical waves which lie in the frequency range 20 Hz to
20000 Hz are called audible or sound waves.These waves are sensitive to
human ear.
- Infrasonic waves The
longitudinal mechanical waves having frequencies less than 20 Hz are
called Infrasonic.These waves are produced by sources of bigger size such
as earthquakes,volcanic eruptions,ocean waves and by elephants and whales.
- Ultrasonic waves The
longitudinal mechanical waves having frequencies greater than 20000 Hz are
called ultrasonic waves. Human ear cannot detect these waves.But certain
creatures like dog,cat,bat,mosquito can detect these waves.Bat not only
detect but also produce ultrasonic.
APPLICATIONS OF ULTRASONIC WAVES
For sending signals.
For measuring the depth
of sea.
For cleaning cloths,
aeroplanes and machinery parts of clocks.
For removing lamp-shoot
from the chimney of factories.
In sterilizing of a
liquid.
In ultrasonography.
In SONAR.
SPEED OF SOUND
The speed of sound
basically depends upon elasticity and density of medium.
Speed of sound in air is
332 m/s, in water is 1483 m/s and in iron is 5130 m/s.
The speed of sound is
independent of pressure i.e., speed remains unchanged by the increase or
decrease of pressure.
The speed of sound in
air increases by 0.61 m/s when the temperature is increases by 10C.
The speed of sound is
more in humid air than in dry air because the density of humid air is less than
the density of dry air.
When sound enters from
one medium to another medium,its speed and wavelength changes but frequency
remains unchanged.
CHARACTERISTIC OF SOUND WAVE
Intensity : Intensity of
sound at any point in space is defined as amount of energy passing normally per
unit area held around that point per unit time.
Loudness depends an
intensity of sound .
Unit of loudness is bel.
Pitch: The pitch of a
sound is the characteristics which distinguishes between a shill and a
grave.Pitch depends upon frequency.
Quality: Quality is that
characteristic of sound which enables us to distinguishes between sound
produced by two sources having the same intensity and pitch.
SHOCK WAVES
A body moving with
supersonic speed in air leaves behind it a conical region of disturbance which
spreads continuously. Such a disturbance is called shock wave.These wave
carries huge energy and may make cracks in window panes or even damage a
building.
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