The Nature of Light

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The Nature of Light

Thomas Young Theory.

Thomas Young was the first person to produce evidence on the wave

nature of light although he was not the first person to suggest that

light had a wave theory, this was also suggested by Christiaan

Huygens.

Experiment: Young’s double slit.

Thomas Young proposed that when two light beams interact they create

interference which can be constructive or destructive. The places

where constructive and destructive interference occur are subjected to

constant change, since electromagnetic waves emitted are capable of

varying phase. Using one light source and splitting it into two beams

you can create two coherent sources, meaning they are of identical

frequencies and have a constant phase difference.

The apparatus consists of a source matching the above requirements, a

screen with two very thin identical slits and a screen to view the

interference on.

In principle, a light bulb, or lamp can be used, but the light must be

reduced to a monochromic source with filters. It can also be done by

splitting the light into its various frequencies using a prism, a

frequency can be selected by channeling the light with a further

screen with only a pin prick in it to allow the light out. These days

lasers are used to provide the light source.

When the light is switched on, it travels up to the first screen and

is split into two beams by the slits, we have seen that when this

happens waves are diffracted and bulge outwards causing two curved

wave fronts to propagate the other side of the slits, at many places

between the slits and the viewing screen there are areas of

constructive interference and by moving the viewing screen it is

possible to get a picture of where they are occurring.

If we could calculate the intensity of the light along the screen (

this could be done by replacing the screen with a instrument such as a

photo-multiplier) we would see the following

Where the greatest intensity occurs at a point equidistant between the

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