Chapter-10|Wave Optics|NCERT 12th Physics:
Proof For Law of Refraction at a Plane Surface(By Huygens’ Wave Theory):
Let after t time a ray comes from B to D and cover a distance V₁t. Now we will form a wavelet at point D. Now, after t time a wave comes from A to C with speed V₂ and cover a distance V₂t, reached at point C. Here we will form another wavelet. The common tangent of point C and D form refracted wavefront.