Transcript Total Internal Reflection - GTU e

G.K.BHARAD INSTITUTE OF
ENGINEERING
Total internal
reflection
Sub : PHYSICS
Sub code: 2110011
Prepared by:
AKABARI VIRAL M.
130590107002
TOTAL INTERNAL REFLECTION
The picture shows the dim
image of a boy formed image
by a glass.
The glass surface is not smooth enough.
 Only very small amount of light is reflected by
the glass.
The environment outside is not dark enough.
Light ray should undergo refraction instead of
reflection.
INTRODUCTION
The inside surface of water or a glass block
can act like a mirror.
1
INTERNAL REFLECTION
A light ray hits the inside face of a
semicircular block as follows.
air
glass
What will happen?
1
INTERNAL REFLECTION
For a small angle of incidence
• The incident ray splits into 2 rays.
• angle of refraction < 90o
air
glass
incident ray
reflected ray
1
INTERNAL REFLECTION
• as angle of incidence ,
angle of refraction 
• eventually, angle of refraction = 90
• angle of incidence = critical angle C
air
glass
incident ray
refracted ray
C
C
reflected ray
1
INTERNAL REFLECTION
• angle of incidence continues to ,
no refracted ray
air
glass
incident ray
reflected ray
1
INTERNAL REFLECTION
• Therefore, if angle of incidence > C,
the light ray is totally reflected inside.
air
glass
incident ray
reflected ray
• This is called total internal reflection.
CRITICAL ANGLE AND REFRACTIVE INDEX
air
glass
refracted ray
C C
incident ray
o
sin
90
n=
sin C
1
n=
or
sin C
reflected ray
C=
sin1
(1)
n
CRITICAL ANGLE AND REFRACTIVE INDEX
• critical angles of different
materials
Refractive
Critical
Medium
index
angle
Glass
1.50–1.70
30–42
Water
1.33
49
Perspex
1.5
42
Diamond
2.42
24
EXAMPLES OF TOTAL INTERNAL
REFLECTION
a Prisms in optical
instruments
• plane mirror = glass + silvered surface
glass
sheet
silvered
surface
forms the
image
• multiple reflection inside the glass
• multiple images formed
O
I1
object
• nuisance in optical instruments
I2
I3
• If light rays strike the inside face at an
angle > 42, glass prism behaves like
a perfect mirror.
45
45
45
45
45
45
• Prisms are used as mirrors in periscopes
and binoculars.
• In single-lens reflex camera
mirror
film
A five-sided ‘pentaprism’ reflects light from
the mirror into the eye.
3
EXAMPLES OF TOTAL INTERNAL
REFLECTION
b Mirage
In a desert.
On a dry road.
3
EXAMPLES OF TOTAL INTERNAL
REFLECTION
b Mirage
• On a hot day, you may see a pool of
water at a distance in a desert.
Hurray!
Sorry! What you see is
just a MIRAGE.
• It happens due to total internal reflections.
Image of
the sky
layers of air near the ground
– hot
– less dense than upper air
– lower refractive indices
Image of
the sky
• light refracted more and more towards
the horizontal
• When light meets a layer of air near
the ground at an angle greater than C,
Image of
the sky
Total internal reflections occurs.
3
EXAMPLES OF TOTAL INTERNAL
REFLECTION
c Light guides
• Light can pass through a curved perspex
rod!
• The rays bounce inside the rod.
• None of them is lost to the air from the
sides.
Applications
1 optical fibre cable
• made up of a bundle of glass fibres
bundle of fibres
glass fibre
2 as a ‘light guide’ for the doctor to see
inside the human body
THANKING YOU