Question

A transparent thin plate of Polaroid is placed on another similar plate such that the angle between their axes is 30⁰. The intensities of the emergent and the unpolarized incident light will be in the ratio of :

• A. 1:4
• B. 1:3
• C. 3:4
• D. 3:8

Answer 1

Answer: (D)

3:8

Answer 2

Let $I_{0}$ be the intensity of unpolarized light, then intensity of light from first transparent thin plate of a Polaroid is

$I = \frac{I_{0}}{2}$

Now, this light will pass through the second similar plate whose axis is inclined at an angle of $30º$ to that of first plate.

According to Malus law, the intensity of emerging light is

$I' = I\cos^{2}30º = \frac{I_{0}}{2}\left( \frac{\sqrt{3}}{2} \right)^{2} = \frac{3}{8}I_{0}\therefore\frac{I'}{I_{0}} = \frac{3}{8}$