What happens to the refracted wavefront when light enters a medium where its speed increases?
**Huygens principle** predicts shape of wavefront after propagation, for point source close spherical, far plane, after reflection from plane mirror spherical wave becomes spherical with centre mirrored, plane wave remains plane but direction changes angle of incidence equals reflection, after passing through thin prism plane wavefront tilts due to different path. When speed increases (e.g., from glass to air), the refracted wavefront bends away from the normal. 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 Bends
Ref: NCERT > Physics Book > Wave Optics > Wavefront and Huygens Principle
