Wave
► A wave is a
disturbance which propagates (transmits) energy from one place to the other
without the transport of the matter.
Waves are broadly of two types
(i)
Mechanical Wave
(ii)
Non-mechanical wave
►Mechanical Wave:
The waves which require material medium (solid, liquid, or gas) for their
propagation (transmit) are called mechanical waves or elastic waves.
Mechanical wave are of two types
(i) Longitudinal wave:
If the particles of the medium vibrate in the direction of propagation of
wave, the wave is called longitudinal wave.
Waves on springs or sound waves in air are examples of
longitudinal waves.
(ii)Transverse Wave: If
the particle of the medium vibrates perpendicular to the direction of
propagation of wave, the wave is called transverse wave.
Waves on
strings under tension, waves on the surface of water are examples of transverse
waves.
► Non-Mechanical wave
or Electromagnetic wave: The waves which do not require medium for
propagation i.e. which can propagate even through the vacuum are called non mechanical
wave.
Light, heat are the examples of non-mechanical wave. In fact
all the electromagnetic waves are non-mechanical.
► All the electromagnetic wave consists of photon.
► The wavelength range of electromagnetic wave is 10-14
to 104.
Properties of
electromagnetic wave:
(i)
They are neutral.
(ii)
They propagate as transverse wave.
(iii)
They propagate with the velocity of light.
(iv)
They contain energy and momentum.
(v)
Their concept was introduced by Maxwell.
Following waves are not electromagnetic.
(i)
Cathode rays
(ii)
Canal rays
(iii)
α rays
(iv)
β rays
(v)
Sound wave
(vi)
Ultrasound wave
Some Important
Electromagnetic Wave
|
Electromagnetic Waves
|
Discoverer
|
Wavelength
(in meter)
|
Frequency range
|
|
γ-Rays
|
Henery Becqueral
|
10-14 to
10-10
|
1020 to
1018
|
|
X- Rays
|
W. Rontgen
|
10-10to
10-8
|
1018 to
1016
|
|
Ultra-Voilet rays
|
Ritter
|
10-8 to
10-7
|
1016 to
1014
|
|
Visible radiation
|
Newton
|
3.9 x 10-7to
7.8 x 10-7
|
1014 to
1012
|
|
Infra-red rays
|
Hershel
|
7.8 x 10-7 to
7.8 x 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
|
Note :
Electromagnetic waves of wavelength range 10-3 m to 10-2 m are called
microwaves.
Phase of vibration: Phase of
vibration of a vibrating particle at any instant is the physical quantity which
expresses the position as well as direction of motion of the particle at that
instant with respect to its equilibrium (mean) position.
Amplitude: Amplitude is defined as the
maximum displacement of the vibrating particle on either side from the
equilibrium position.
Wavelength: Wavelength is the distance
between any two nearest particle of the
medium, vibrating in the same phase. It is denoted by the Greek letter Lembda (λ).
In
transverse wave distance between two consecutive crests or troughs and in
longitudinal wave, distance between two consecutive compressions or rarefaction
is equal to wavelength.
Relation between
wavelength, frequency and velocity of wave
Velocity of wave = frequency x wavelength or, v = nλ.
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