By corpuscular theory of light, the phenomenon which can be explained is

Figure shown plane waves refracted for air to water using Huygen's principle $a, b, c, d, e$ are lengths on the diagram. The refractive index of water wrt air is the ratio.

Light emerges out of a convex lens when a source of light kept at its focus. The shape of wavefront of the light is:

Explain the use of wavefront to understand wave propagation. 

The idea of secondary wavelets for the propagation of a wave was first given by

Explain the reflection of plane wavefront from concave mirror.