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Wave Optics

JEE Main level, numerical answer, medium

172 of 191

Question 172 of 191

As shown in figures, three identical polaroids ${P}_{1}$ , ${P}_{2}$ and ${P}_{3}$ are placed one after another. The pass axis of ${P}_{2}$ and ${P}_{3}$ are inclined at angle of $60º$ and $90º$ with respect to axis of ${P}_{1}$ . The source $S$ has an intensity of $256W{m}^{-2}$ . The intensity of light at point $O$ is _____ $W{m}^{-2}$ .

Show answer and solution

Answer: 24

As given here, the pass axis of

{P}_{2}

and

{P}_{3}

are inclined at angle of

60º

and

90º

with respect to axis of

{P}_{1}

.
Therefore, intensity of light after falling on first polaroid

{P}_{1},{I}_{1}=\dfrac{{I}_{0}}{2}

Intensity of light after falling on second polaroid

{P}_{2},{I}_{2}={I}_{1}{\cos }^{2}60^{\circ}=\dfrac{{I}_{0}}{8}

Intensity of light after falling on third polaroid

{P}_{3},{I}_{3}={I}_{2}{\cos }^{2}30^{\circ}=\dfrac{{I}_{0}}{8}\left(\dfrac{3}{4}\right)=\dfrac{3{I}_{0}}{32}

The intensity of light at

O

\dfrac{3{I}_{0}}{32}=\dfrac{3\times 256}{32}=24W{m}^{-2}

JEE Main question paper PDF

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JEE Main 2025 Apr 2 Shift 1 question paper

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