#unpolarized light

Optical Phenomena and Applications

What causes the intensity to vary when a second polaroid is rotated in front of another polaroid through which unpolariz

**Convex lens focusing** plane wave into point because lens introduces phase delay proportional to thickness, converting plane wavefront to spherical converging to focal point, property ensures rays parallel to axis meet at focus, spherical aberration minimized for paraxial rays, lensmaker's formula determines focal length. The first polaroid polarizes the light linearly, and the second allows only the component of the electric field aligned with its pass-axis, varying with the angle via Malus’ law. 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

Ref: NCERT > Physics Book > Wave Optics > Optical Phenomena and Applications

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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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Polarization and Malus Law

What is the nature of unpolarized light?

**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°. Unpolarized light has electric vectors oscillating in all directions in the plane perpendicular to the propagation direction, random

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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Wavefront and Huygens Principle

Why does the intensity of transmitted light through a polaroid decrease when rotated, even if the incident light is unpo

**Wavefront types** point source spherical, distant point source plane, after convex lens plane wave focuses to point because lens adds phase delay proportional to thickness, converging spherical wavefront, after concave mirror plane wave becomes spherical converging to focus, illustrating Huygens construction. Unpolarized light becomes polarized after the first polaroid, and the second polaroid’s pass-axis alignment determines the transmitted component, reducing intensity as the angle increases. 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 = 2

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

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