Hello students today we'll discuss about
principle of reversibility of light so
let us start that
students let's start with the principles
of reversibility of light the statement
is
if a ray of light undergoes the number
of reflections and refractions maybe
reflections maybe refraction by both and
if following certain paths and if the
direction of light is reversed then it
follows the same path it has traveled
earlier
what is the meaning of this suppose I
have a medium air here and another
medium say water here now light falls on
this in the interface of air and water
now it bends toward novel because you
are to being a denser medium it follows
this Fox suppose I keep a mirror over
here perpendicular to this so that the
refracted ray incident normally to the
mirror then we know that from the
principle of reflections that anyway in
finding normal we return back to the
same medium in the same direction for
you to change the direction it will get
reversed the direction is reversed now
therefore it will move in this direction
after reflections to move in this
direction and he says that if the
direction of light is reversed you can
see that is the direction of ray of
light after refraction is reversed or
reflection in rivers then from here it
is river and then it will follow the
same path and emerge from this line only
it is not going to come out from any
other directions only this part so this
path is called this principle is called
principle of reversibility or that means
the ray of light reverses this direction
and follows the same path that it is to
followed earlier so if I say that it
goes from air to water following this
path then it has to come follow the same
path if it is sent from this video
and from this point in this direction
cinta raises reflected back in this
direction then in the form of the same
part redress is the same part this is
called principle of reversibility to
light from this we can conclude that
that neo mu of air here or knew of water
here this is a new hair this is me water
then from here we said that if I apply
Snell's law then I'll write mu of water
with respect to air is Sinai upon sine R
I is the angle of incidence and odd is
the angle of destruction if I if the
wave follows the reversible path so for
this case this is I and this is R so
this is the equation I am going to use
if this is air and water it follows the
same path that means if I send it back
in the opposite direction from here then
this is going to follow this path this
again this reaches is this path so for
this if I write the patient for the MU
of air with respect to water this will
be sine of r by sine of i so if you
multiply these two together and again
powa in to mu
aw equal to 1 okay this is known as
principle of usually
