ELECTRO MAGNETIC RAIATIONS

1. BY-
SYED MASOOD

2.  These are the waves in the sense that they
consists of regular sinusoidal variations of electric
& magnetic field at right angle to one another.

3. Electromagnetic radiation is
classified according to the frequency
of its wave.
In order increasing frequency and
decreasing wavelength,
radio waves,
microwaves,
infrared radiation,
visible light,
ultraviolet radiation,
X-rays and
gamma rays
Its also called electro magnetic spectrum.
The eyes of various organisms sense a small
and somewhat variable window of
frequencies called the visible spectrum.

4.  E.M.R are produced by the movement of
electrons within the atom.
 When any energy is added i.e by heat or
stimulus .
an electron to move out to a higher energy
electron shell.
 When electron returns to the normal level
the energy is release as a pulse of
E.M.energy.
Cause

6. 1. Wavelength-
A wave consists of successive troughs and crests
The distance between two adjacent crests or troughs is
called the wavelength.
Waves of the electromagnetic spectrum vary in size-
very long - Radio waves the size of buildings
to
very short gamma rays smaller than atom nuclei.
Frequency is inversely proportional to wavelength
 where v =speed of the wave
f = frequency
λ is the wavelength.
As waves cross boundaries between different media, their speeds change
but their frequencies remain constant.

7. 2) Interference-
 Interference is the superposition of two or
more waves resulting in a new wave
pattern.
 If the field are in the same direction, they
constructively interfere,
while opposite directions cause destructive
interference.
 The energy in electromagnetic waves is
sometimes called radiant energy.

8. 3) RECTILINEAR
PROPAGATION
radiations travel in
straight lines in the space.
Emr are emitted from their
source in all direction.
 Obey
I = 1/D2
here I= intensity&
D= distance.

9. 4) PHASE
DIFFERENCE-
WHEN stimulated light
emission i.e LASER is
possible to make all
the emitted atom
radiate in one phase.
5) COHERENCE-
The peak & trough of
electric & magnetic
radiation travel in the
same direction & same
time.

10. 6) REFLECTION-
when an
electromagnetic wave
encounters a medium
which will not transmit
it.
 The ray is reflected
back in the same
plane such that

11.  Internal reflection-
occurs when the angle i
strikes an interface b/w
the 2 media in such that
instead of transition its
reflected.
 This happens at the
angles of incidence
above

12. 7) REFRACTION-
it occurs when
E.M.R are transmitted
from one medium to
another with an angle
of incidence
GREATER THAN
ZERO.
 Rays with a 0 angle of
incidence i.e striking
the surface at rt
angles continue in the
same line.

13.  Acc
refraction occurs when the
rays is deflected from its
original course by an
amount depending on the
media involved & the angle
of incidence.
denser media= Refracted
towards the normal.
Less dense media =
refracted away the normal.
Less
dense
Dense
Less
dense

14.  Refraction is imp when using
hydrotherapy as a form of
treatment.
 As the refraction of rays passing
from water the air makes the
position of object in water difficult to
assess.
the same is true when using water as
coupling medium for ultrasound.

15. 8) ABSORPTION-
When E.M.R rays strike a new
medium they may be absorb &
produce an effect
( LAW OF GROTHUS).
 The proportion of rays depends
upon-
 wavelength of rays.
 nature of medium.
 angle of incidence.
There are following media that
absorbs various E.M.R.

16.  Window glass- visible light , IRR.
 WATER= IRR, visible, U.V.
 Soft tissue= X rays.
 Cello phone= short U.V rays.
the angle at which the rays strike the surface
also affects the proportion of absorption.

17. It depends on the COSINE LAW
it states that the intensity of
rays at a surface varies with
the cosine of angle b/w the
incident rays & the normal.
 Cosine 90= 0
no absorption.
 cosine 0= 1
max absorption
Cosine 90= 0
no absorption.
cosine 0= 1
max absorption

18. 9) SCATTERING-
Radiation passing in non
homogenous matter
may be partly scattered
that is the direction of some
rays is altered effectively
reducing the depth of
penetration.
The scattered radiation may
travel in difference direction
& be absorbed at some
point away from the main
beam of radiation.

19. reflection.
refraction.
E.g.- U.V are strongly
scattered in the skin
decreasing their
penetration.
.