What is the shape of the wavefront in each of the following cases:
(a) Light diverging from a point source.
(b) Light emerging out of a convex lens when a point source is placed at its focus.
(c) The portion of the wavefront of light from a distant star intercepted by the Earth.

Explanation

(a) Spherical
(b) Plane
(c) Plane (a small area on the surface of a large sphere is nearly planar).