JEE Main · 2023 · 31 Jan 2023 · Shift 1 · Wave Optics

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Two polaroide A and B are placed in such a way that the pass-axis of polaroids are perpendicular to each other. Now, another polaroid C is placed between A and B bisecting angle between them. If intensity of unpolarised light is

I_{0}

then intensity of transmitted light after passing through polaroid B will be :

(A) $\frac{I _{0}}{4}$
(B) $\frac{I _{0}}{2}$
(C) $\frac{I _{0}}{8}$ ✓ Correct
(D)Zero

Answer: (C)

Solution

Unpolarised light of intensity

I_{0}

loses half its intensity on crossing the first polaroid A, leaving

\frac{I _{0}}{2}

polarised along A's axis. The middle polaroid C bisects the

9 0^{\circ}

between A and B, so it stands at

4 5^{\circ}

to A; by Malus's law the light emerging from C is

\frac{I _{0}}{2} cos^{2} 4 5^{\circ} = \frac{I _{0}}{4}

. B is a further

4 5^{\circ}

from C, so after B the intensity is

\frac{I _{0}}{4} cos^{2} 4 5^{\circ} = \frac{I _{0}}{8}

JEE Main · 2023 · 31 Jan 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 31 Jan 2023 · Shift 1 · Wave Optics

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