2. TOTAL INTERNAL
REFLECTION
What is it?
∆ We know that, when light enters from one
medium to the other, such that both of them have
vivid optical densities, then the light gets refracted.
∆ But does this happen every time?
∆ Let’s make some adventure to figure it out!!
3. Now we’ll study 3 different cases of the light ray as it
enters from an optically denser to a rarer medium.
#CASE {1}
4. # CASE {2}
Critical Angle:-
Measure of an incident
angle, for which the
angle of refraction is
equal to 90°.
Here angle of incidence
= critical angle, so the
light ray overlaps the
interface , and also gets
5. # CASE {3}
Here angle of
incidence is greater
than critical angle
So, the light ray gets
totally reflected back
in the same medium
from which it was
incident.
This phenomenon is
6. FINDING CRITICAL ANGLE
∆ From snell’s law we have,
n21 =sin i /sin r
∆ So, n12=sin r/sin i
∆ In TIR, angle r=90°(sin 90 =1)
∆ Hence, n12=1/sin i
∆ Finally, sin i= 1/n12
7. NOW LET US STUDY SOME
APPLICATIONS OF TOTAL
INTERNAL REFLECTION!
8. FORMATION OF RAINBOW
It is a natural
phenomenon which is
a combination of
Refraction, total
internal reflection and
dispersion.
9. LUSTEROF DIAMOND
The diamond is cut suitably ,so
that the light entering the
diamond from any face,
incident at an angle greater
than its critical angle and
undergoes multiple total
internal reflection at various
surfaces. The critical angle for
diamond is 24.4°.
10. MIRAGE
It is an optical illusion which
is responsible for the
appearance of the water layer
at short distances in a desert
or on the road. Mirage is an
example of total internal
reflection which occurs due
to atmospheric refraction.
12. OPTICAL FIBER
Electrical or radio signals are converted to optical
Signals and then passed through the optical fibre
undergoing total internal reflection .They are then
transmitted in the form of electrical signals.
13.
14. QUESTIONTIME
1) Mirage occurs due to Total
Internal Reflection. True or
False?
2) What is the critical angle of
diamond?
3) Name the 3 phenomena
involved in the formation of
rainbow.
4) Name any one condition needed
for TIR.
15. SOLUTIONS
1) True
2) 24.4
3) Refraction, TIR, Dispersion
4) Light should be incident from denser to a rarer
medium.
5) n= 1/sin i c
n=1/sin 45°
n=1/1/√2
n=√2 or 1.42
