What characteristic of light waves allows a convex lens to transform a plane wave into a converging spherical wave?
**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. The wave nature enables the lens to delay the wavefront variably across its surface, curving it into a spherical shape that converges at the focal point. 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
Ref: NCERT > Physics Book > Wave Optics > Wavefront and Huygens Principle