JEE Advanced 2024 Paper 1 · Q10 · Polarization
A point source $S$ emits unpolarized light uniformly in all directions. At two points $A$ and $B$, the ratio $r = I_A/I_B$ of the intensities of light is 2. If a set of two polaroids having $45^\circ$ angle between their pass-axes is placed just before point $B$, then the new value of $r$ will be _____.
Reveal answer + step-by-step solution
Correct answer:8
Solution
Original ratio: $I_A/I_B = 2$. The first polaroid takes unpolarized light and transmits half of it (factor $1/2$). The second polaroid (at $45^\circ$ to the first) transmits $\cos^2 45^\circ = 1/2$ of the light from the first. Net transmission factor through the two polaroids = $(1/2)(1/2) = 1/4$. New intensity at $B$: $I'_B = I_B/4$. New ratio: $I_A/I'_B = 2/(1/4) = 8$. Hence $r' = 8$.
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