The figure shows a surface XY separating two transparent media, medium -1 and medium -2. The lines ab and cd represent wavefronts of a light wave travelling in medium-1 and incident on XY. The lines ef and gh represent wavefronts of the light wave in medium-2 after refraction.
The phases of the light wave at c, d, e and f are ϕc, ϕd, ϕeand ϕfrespectively. It is given that ϕc ≠ ϕf