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#intensity reduction

2 public questions tagged with this topic.

Polarization and Malus Law

What is the intensity of light after passing through two polaroids with pass-axes at \( 75^\circ \), if the initial unpo

**Two polaroids** with pass-axes perpendicular intensity zero because second blocks component, with 45° intensity I₀/4 if initial after first I₀, if initial unpolarized I₀, after first I₀/2 then after second at 45° I₀/4. Three polaroids first and third crossed 90°, middle at 45° maximum transmission because middle rotates polarization, I after first I₀/2, after middle at 45° I₀/4, after third at 45° to middle I₀/4×cos²45°= I₀/8, non-zero, maximum when middle 45°. After the first polaroid, I = (I₀/2) . After the second at 75° , I = (I₀/2) cos² 75° . cos 75° ≈ 0.259 , I = (I₀/2) × (0.259)² = (I₀

Ref: NCERT > Physics Book > Wave Optics > Polarization and Malus Law

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Wavefront and Huygens Principle

What is the intensity of unpolarised light after passing through a single polaroid, if the initial intensity is \( I_0 \

**Wavefront** is locus of points in same phase, spherical from point source, plane at large distance because radius large, Huygens principle every point on wavefront acts as secondary source of wavelets, new wavefront envelope of secondary wavelets, allows prediction of new wavefront shape from known wavefront, explains reflection and refraction. Unpolarised light has its intensity reduced to half after passing through a polaroid, so I = (I₀/2) . Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, sinC = 1/n, λ' = λ/n and A = 2a cos(φ/2), calculation gives (I₀/2), illustrating

Ref: NCERT > Physics Book > Wave Optics > Wavefront and Huygens Principle

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