Light travels in a straight line but is it possible to trap light and drag it in any direction?

What you need:

A transparent plastic bottle, water, a torch and an empty bowl

What you do:

Make a hole on one side of the bottle, a little below the centre.

Holding a finger against the hole, fill the bottle with water and then take it to a dark room.

Shine a torch on the bottle on the side opposite the hole and take off your finger from the hole. The water will spill out through the hole into the bowl.

What do you see?

You can see the water carrying some of the light from the torch through the bottle and into the bowl.

How does this happen?

When light strikes the internal surface of water from below, some of it passes through and some get reflected. The amount of light reflected depends on the angle of the light rays. If all the light is reflected, it is called Total Internal Reflection. The angle at which light from the torch strike the inner surface of the stream of water leaving the bottle determines whether or not the light remain trapped in the stream through Total Internal Reflection.

The most important application of Total Internal Reflection is in the making of optical fibres. Light travelling through these fibres can be rolled, twisted or turned and hence the fibres are most useful in the telecommunication industry and in physics experiments, where light has to be transported through large distances (especially from laser sources).

The sparkle of a diamond and the reflection of a cat’s eye (road reflector) occurs because of Total Internal Reflection.

 

Picture Credit : Google

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