Wave Optics - Diffraction

Description:

When the light bends and enters the shadow areas on crossing the obstruction this phenomenon is known as Diffraction. Diffraction is only possible because of the wave nature of light.

Note − Light only bends into the shadow region.

Diffraction shows that light does not travel in a straight line, instead it spreads in all direction also proving the wave nature of light.

Diffraction can be studied using the following experiment:

The experiment consists of a source of light (S), an obstacle with a small opening (AB) of width ‘a’, and a screen. The light wave passes through the opening AB and gets diffracted.

• O is a point where the phase difference of waves from A and B is zero, so there is a constructive superposition and it becomes a bright point and path difference is 3λ/2.

• P is a point on the screen which is dark and we find the path difference between AP and BP is 1λ.

• The angle of elevation of point P from the point O is θ = λ/a

• The distance of the first dark point on the screen is X = λD/a