JEE Main · 2013 · 07 Apr 2013 · Offline · Wave Optics

A beam of unpolarised light of intensity

I_{0}

is passed through a polaroid A and then through another polaroid B which is oriented so that its principal plane makes an angle of

4 5^{\circ}

relative to that of A. The intensity of the emergent light is:

(A) $I_{0} /2$
(B) $I_{0} /4$ ✓ Correct
(C) $I_{0} /8$
(D) $I_{0}$

Answer: (B)

Solution

Unpolarised light loses exactly half its intensity on crossing the first polaroid, so after A the beam carries

I_{0} /2

and is now plane polarised along A's axis. Malus's law then decides what gets through B, whose axis is tilted at

4 5^{\circ}

: the transmitted intensity is

\frac{I _{0}}{2} cos^{2} 4 5^{\circ} = \frac{I _{0}}{2} \cdot \frac{1}{2} = \frac{I _{0}}{4}

JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option

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