1. LAWS GOVERNING
RADIATION
Prof. Dr. M. Rajesh, PT, M.P.T(cardio), B.C.R.C
TRINITY MISSION AND MEDICAL FOUNDATION
MADURAI

2. INTRODUCTION
 Rays are obeyed some laws when travel from one medium to
another.
 Infrared visible and ultraviolet waves travel in straight lines until
they encounter a different medium when they may be
transmitter reflected or absorbed.

3. REFLECTIONS
 A normal is a line drawn perpendicular to the surface of a
medium at the point where an electromagnetic waves strikes.
 Angles of reflection are refraction are measured between
electromagnetic Ray and the normal.
 Reflection occurs when an electromagnetic wave encounters
medium which will not transmit it. In this case the ray is
reflected back in the same plane such that the angle between
the incident ray and the normal equals the angle between the
reflected ray and the normal.

4.  The laws of reflection are employed in the design of reflectors
used for the redirection of Rays towords and appropriate
targets. In in infrared and ultraviolet light lamps parabolic
reflector is normally used as this avoids the danger of the
concentration of rays which occurs with some m shape of
reflectors.

5.  A parabolic reflectors collects all the rays traveling in the in
appropriate direction and reflects them from its surface so that
they even surely all image parallel. It should be remembered
however that the majority of rays emitted forwards from these
lamps come directly from the source and so diverge. only a
small proportion are reflected in the above way.


6. INTERNAL REFLECTION
 Internal reflection occurs when the angle of incidence of rays
strikes and interface between two media is such that instead of
being transmitted, it is affected. This happens at angles of
incidence above a certain critical angle. Internal reflection in
quartz is used to cause ultraviolet to pass down especially cut
quartz rod and be limited only from the end. This method of
application is used when ultraviolet is applied to an internal
cavity are and infected sinus.

7. REFRACTION
 Refraction When electromagnetic rays are transmitted from one
medium to another with an angle of incidence greater than
zero. Rays with zero angle of incidence that is striking surface at
right angles continue in the same straight line.
 Refraction causes the rate to be deflected from its original
course by an amount depending on the medium involved and
the angle of incidence for example snell's law. When passing
into an optically denser medium the ray is refracted towards the
normal. When passing into a less dense medium it is refracted
away from the normal.

8.  This is so in wave refraction occur in glass and air medium.
Refraction is important when using hydrotherapy as a form of
treatments as refraction rays passing from water to makes the
position of objects in the water difficult to assess. The same is
true when using water coupling medium for ultrasound.

9. ABSORBTION
 When electromagnetic rays strikes a new medium they may be
absorbed and thus produced and effects example law of
Grothus.
 The proportion of rays absorbed depends upon the wavelength
of the rays the nature of the medium and the angle of
incidence. The absorption involves an interaction between their
magnetic and electromagnetic are electric fields of the the
electromagnetic radiation and the orbital electron field around
the atoms of the media.

10.  A filter is medium which will absorb some electromagnetic
waves while allowing others to pass. Window glass allows visible
light and infrared rays to pause while observing ultraviolet rays.
Water absorbs infrared but allows visible and ultraviolet to pass.
X rays are passed through the soft tissues on to a photography
plates but are observed to a great extent by bone. Cellophane
absorbs short ultraviolet rays while growing long once to pause.
 The cosine law which states that the intensity of rays at surface
where is with the crossing of the angle between them incident
ray and the normal.

11.  In practical terms this means that if the angle of incidence is 90
degree then no rays will be observed as they will be traveling
parallel to the surface. If the angle of incidence is zero degree
then the rays are striking the surface so as to make a right angle
with each and the maximum number will be absorbed. Therefore
when applying ultraviolet and infrared Radiation greater rays
should we made ensure that the maximum number of rays strikes
the surface of the 90 degree.

12. Electromagnetic waves being produced from the point source
also obey the law of inverse square law. This states that the
intensity of the race from the point source where is inversely
with the square of the distance from that point source. Rays
produced from yah point source diverge from one another at a
uniform rate. If for example acid number of race cover a square
with sides of 1 metre at a distance of 1 metre from the source
at a two metres they will cover a square with sides 2 metre
long.

13. 
Ultraviolet lamps and some infrared lamps act almost as point
sources the race they generate over the law of inverse squares.
In practical terms this means that the closer a patient is to the
source the greater is the intensity of the radiation being
received at any one point of the skin.

Certain situations moving the lamp closer will hello shorter dose
to be given for example if you are dose of the ultraviolet of 60
seconds at 100 centimetres produces a certain effects full stop
the same effect would be obtained in 15 seconds at a distance
of 50 cm that is one quarter of the time at half the distance.


14. THANK YOU
Prof. Dr. M. RAJESH, PT,M.P.T(cardio),B.C.R.C
TRINITY MISSIOIN AND MEDICAL FOUNDATION
MADURAI.
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