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2 public questions tagged with this topic.

Refraction, Refractive Index and Critical Angle

Why does the wave theory of light predict that the speed of light decreases when it bends towards the normal during refr

**Critical angle** sinC = n₂/n₁, n₁ denser, n₂ rarer 1 for air, for C=36.9° n₁=1/sin36.9°=1/0.6=1.67, for C=39° n=1/sin39°=1/0.629=1.59, for n=1.85 C=arcsin(1/1.85)=arcsin0.5405=32.7°, total internal reflection occurs only when light travels from denser to rarer and incidence > C, because Snell's law would require sinθ₂>1 impossible. The wave theory suggests that light slows down in a denser medium, causing the wavefront to bend towards the normal as it takes less time to travel a shorter path in the slower medium. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, sinC = 1/n,

Ref: NCERT > Physics Book > Wave Optics > Refraction, Refractive Index and Critical Angle

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Wavefront and Huygens Principle

Why does the wave theory predict that light bends towards the normal when entering a medium where its speed is lower?

**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. The wavefront tilts towards the normal because the part entering the slower medium lags, reducing the angle of propagation relative to the boundary. 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 Wavefront

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

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