g.k.bharad institute of engineering prepared by: akabari viral m. 130590107002 sub : physics sub...
TRANSCRIPT
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