Question

Plane polarised light is passed through a polaroid. On viewing through the polaroid we find that when the polaroid is given one complete rotation about the direction of the light, one of the following is observed

[MNR 1993]

• A. The intensity of light gradually decreases to zero and remains at zero
• B. The intensity of light gradually increases to a maximum and remains at maximum
• C. There is no change in intensity
• D. The intensity of light is twice maximum and twice zero

Answer 1

The correct option is D

The intensity of light is twice maximum and twice zero

Let us take a general case, in the figure below: (the direction of propagation of light is perpendicular to the plane of your screen)

Suppose we start turning the polaroid clockwise, the electric field will come inline with the transmission axis after some time, resulting in maximum intensity. Again after 180${}^{\circ }$ there will be maximum intensity. Similarly, there will be two zero intensity cases also in one rotation, corresponding to the electric field and transmission axis becoming perpendicular.