Question

If an unpolarised light is converted into plane polarised light using a polaroid, its intensity becomes

• A. half
• B. one-fourth
• C. one-third
• D. one-eighth

Answer 1

Answer: (A)

half

Answer 2

Unpolarized light consists of waves whose electric field vectors oscillate in all possible directions perpendicular to the direction of propagation. A polaroid sheet acts as a filter that allows light waves vibrating only in a specific direction (its transmission axis) to pass through. When unpolarized light encounters a polaroid, on average, only half of the randomly oriented electric field vectors will be parallel to the transmission axis. These components pass through, while the others are blocked. Thus, the intensity of the transmitted light is half the intensity of the incident unpolarized light.

Mathematically, if $I_0$ is the intensity of unpolarized light incident on a polaroid, the intensity of the plane-polarized light emerging from it is: $I = \frac{1}{2} I_0$