Question-46 Three polarised sheets are co-axially placed. Pass axis of polaroids 2 and 3 make 30^\circ and 90^\circ with pass axis of polaroid sheet 1. If I_0 is the intensity of unpolarised light entering sheet 1, the intensity of the emergent light through sheet 3 is
(A) zero
(B) \frac{3I_0}{32}
(C) \frac{3I_0}{8}
(D) \frac{3I_0}{16}
Answer : (B)
Explanation:
According to Malus’ law,
I = I_0 \cos^2 \theta
When beam passed through polaroid 1,
I = \frac{I_0}{2}
When beam passed through polaroid 2,
I₂ = \frac{I_0}{2} \cos^2 60^\circ
∴ I₂ = \frac{I_0}{8}
When beam passed through polaroid 3,
I₃ = \frac{I_0}{8} \cos^2 30^\circ = \frac{I_0}{8} \times \left(\frac{\sqrt{3}}{2}\right)^2 = \frac{3I_0}{32}