A light ray incident on a glass block
A light ray incident on a glass block bends towards the normal and while it leaves it bends back again away from the normal.
Light travels at different speeds in different materials.
Light travels at 3 × 108 m/sec in vacuum, at a slightly lower speed in air and at 2 × 108 m/sec in glass.
In diamond, light travels at about 40% of its speed in vacuum. When light travels from one medium to another, its speed changes.
This change causes light rays to bend.
Thus when light bends in passing from one medium to another, we call the process as refraction.
that water or glass is transparent.
But when water is running down a faucet, we can see the water stream.
Isn’t it? The reason is: Even though water or glass are transparent to visible light, we can “see” them only at their edges, where the refraction conditions are pronounced.
If there is a uniform sheet of glass or water in front of us, it would be difficult to see them.
Don′t we sometimes wonder if the car windscreen is wound up or down?
In quite a lot of public places, such as hospitals, plain glass doors are marked with a horizontal white bar – so that persons do not try to walk through the door!
A transparent substance in which light travels is known as a medium.
Air, glass, water, ice, diamond etc., are all examples of medium.
Different media are said to have different optical densities.
A medium in which speed of light is more when compared with other medium is known as optically rarer medium.
is an optically rarer medium as compared to water, glass and alcohol.
A medium in which speed of light is less when compared with other medium is known as optically denser medium.
Glass is optically denser medium than air and water.
When a ray of light goes from a rarer medium to a denser medium, it bends towards the normal (at the point of incidence).
When a ray of light goes from a denser medium to a rarer medium, it bends away from the normal (at the point of incidence).