G.K.BHARAD INSTITUTE OF ENGINEERING

Prepared by:AKABARI VIRAL M.

130590107002

Sub : PHYSICSSub code: 2110011

Total internal reflection

The picture shows the image of a boy formed 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.

dim image

The inside surface of water or a glass block can act like a mirror.

A light ray hits the inside face of a semicircular block as follows.

What will happen?

airglass

• The incident ray splits into 2 rays.• angle of refraction < 90o

incident ray reflected ray

refracted ra

y

airglass

For a small angle of incidence

incident ray reflected ray

airglass

C C

• as angle of incidence , angle of refraction

• eventually, angle of refraction = 90

refracted ray

• angle of incidence = critical angle C

no refracted ray

reflected ray

airglass

• angle of incidence continues to ,

incident ray

• Therefore, if angle of incidence > C, the light ray is totally reflected inside.

reflected ray

airglass

incident ray

• This is called total internal reflection.

incident ray reflected ray

airglass

C C

refracted ray

sin 90o

sin Cn =

1 sin C

n = C = sin1or 1 n

( )

• critical angles of different materials Medium

Refractive index

Critical angle

1.50–1.70 30–42Glass

Water

Perspex

Diamond

1.33 49

1.5 42

2.42 24

a Prisms in optical instruments

• plane mirror

= glass + silvered surface

glass sheet

silvered surface

forms the image

I1 I2 I3O objec

t

• multiple reflection inside the glass• multiple images formed

• nuisance in optical instruments

4545

•If light rays strike the inside face at an angle > 42, glass prism behaves like a perfect mirror.

4545

4545

•Prisms are used as mirrors in periscopes and binoculars.

• In single-lens reflex camera

A five-sided ‘pentaprism’ reflects light from the mirror into the eye.

filmmirror

b Mirage

On a dry road.

In a desert.

b Mirage

Hurray!

• On a hot day, you may see a pool of water at a distance in a desert.

Sorry! What you see is just a MIRAGE.

• It happens due to total internal reflections.

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

Image of the sky

• When light meets a layer of air near the ground at an angle greater than C,

Total internal reflections occurs.

Image of the sky

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

2 as a ‘light guide’ for the doctor to see inside the human body

1 optical fibre cable• made up of a bundle of glass fibres

glass fibre

bundle of fibres