As shown in figures, three identical polaroids P₁, P₂ and P₃ are placed one after another. The pass axis of P₂ and P₃ are inclined at angle of 60° and 90° with respect to axis of P₁. The source S has an intensity of 256 W m⁻². The intensity of light at point O i s ____ W m⁻².
Physics · Wave Optics · polarisation
JEE Mains 29 January 2023 Shift 1 Morning Shift

Question

As shown in figures, three identical polaroids P₁, P₂ and P₃ are placed one after another. The pass axis of P₂ and P₃ are inclined at angle of 60° and 90° with respect to axis of P₁. The source S has an intensity of 256 W m⁻². The intensity of light at point O i s ____ W m⁻².

Physics · Wave Optics · polarisation

JEE Mains 29 January 2023 Shift 1 Morning Shift

G1 Physics · Accepted Answer

After the first polaroid, intensity becomes 256/2 = 128 W m⁻². Through P₂, multiply by cos²60° = 1/4, giving 32 W m⁻². The angle between P₂ and P₃ is 30°, so through P₃ multiply by cos²30° = 3 4 \frac{3}{4} 4 3 ​ . Final intensity = 32× 3 4 \frac{3}{4} 4 3 ​ = 24 W m⁻².