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G.K.BHARAD INSTITUTE OF ENGINEERING. Total internal reflection. Sub : PHYSICS Sub code: 2110011. Prepared by: AKABARI VIRAL M. 130590107002. Total internal reflection. dim image. Only very small amount of light is reflected by the glass. The glass surface is not smooth enough.
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G.K.BHARAD INSTITUTE OF ENGINEERING Total internal reflection Sub : PHYSICS Sub code: 2110011 Prepared by: AKABARI VIRAL M. 130590107002
dim image Only very small amount of light is reflected by the glass. The glass surface is not smooth enough. The environment outside is not dark enough. Light ray should undergo refraction instead of reflection. The picture shows the image of a boy formed by a glass.
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 refracted ray 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 refracted ray air glass C C incident ray reflected ray
1 Internal reflection • angle of incidence continues to , norefracted 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 1 sin 90o sin C sin C C C 1 ( ) n refracted ray air glass incident ray reflected ray n = C = sin1 n = or
Critical angle and refractive index Refractive index Critical angle Medium Glass 1.50–1.70 30–42 Water 49 1.33 Perspex 1.5 42 Diamond 2.42 24 • critical angles of different materials
Examples of total internal Reflection a Prisms in optical instruments • plane mirror = glass + silvered surface glass sheet silvered surface forms the image
I1 I2 I3 O object • multiple reflection inside the glass • multiple images formed • nuisance in optical instruments
45 45 • If light rays strike the inside face at an angle > 42, glass prism behaves like a perfect mirror. 45 45 45 45
film mirror • In single-lens reflex camera 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 aMIRAGE.
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.
bundle of fibres glass fibre Applications 1 optical fibre cable • made up of a bundle of glass fibres 2 as a ‘light guide’ for the doctor to see inside the human body
