A parallel beam of light strikes a piece of transparent glass having cross section as shown in the figure below. Correct shape of the emergent wavefront will be (figures are schematic and not drawn to scale)-

By Huygen's wave theory of light, we cannot explain the phenomenon of

Wave front is locus of all the points where the particles of the medium vibrate with the same

Explain the use of wavefront to understand wave propagation. 

On a hot summer night, the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally, the Huygens' principle leads us to conclude that as it travels, the light beam