Why does the wave model predict that light bends away from the normal when entering a rarer medium?
**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. In a rarer medium, light speeds up, causing the wavefront to tilt away from the normal as it takes less time to travel a longer path. 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
Ref: NCERT > Physics Book > Wave Optics > Optical Phenomena and Applications