Three identical polaroids P₁, P₂ and P₃ are placed one after another. The pass axis of P₂ and P₃ are inclined at an angle of 60° and 90° with respect to axis of P₁. The source has an intensity 256 W/m². The intensity of light at point ' O ' is (cos 30° = √(3)/2, cos 60° = 0.5) (a) 24 W/m² (b) 20 W/m² (c) 16 W/m² (d) 8 W/m²

Answer: (a). After P₁: 256/2 = 128 W/m² After P₂ ( 60°): 128cos ² 60° = 32 W/m² After P₃ ( 30° to P₂): 32cos ² 30° = 32 × 3/4 = 24 W/m² So the answer is (a) 24 W/m².

Three identical polaroids P₁, P₂ and P₃ are placed one after another… | MHT CET 2025 (19 Apr, Shift 1)

Q21MHT CET 2025 · 19 APR · SHIFT 1Medium

Polarisation

Three identical polaroids $P_1, P_2$ and $P_3$ are placed one after another. The pass axis of $P_2$ and $\mathrm{P}_3$ are inclined at an angle of $60^\circ$ and $90^\circ$ with respect to axis of $\mathrm{P}_1$ . The source has an intensity $256\text{ W/m}^2$ . The intensity of light at point ' O ' is $\left(\cos 30^\circ = \sqrt{3}/2, \cos 60^\circ = 0.5\right)$

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Answer: (a)

After $P_1$ : $\frac{256}{2} = 128\ \text{W/m}^2$
After $P_2$ ( $60^\circ$ ): $128\cos^2 60^\circ = 32\ \text{W/m}^2$
After $P_3$ ( $30^\circ$ to $P_2$ ): $32\cos^2 30^\circ = 32 \times \frac{3}{4} = 24\ \text{W/m}^2$
So the answer is (a) $24\ \text{W/m}^2$ .

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Polarisation question from MHT CET 2025 (19 Apr, Shift 1)

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