What is the shape of the wavefront in each of the following cases ?
(a) light diverging from 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 earth.

Explanation

The wavefront on earth for the sunlight (treated as point source) will be spherical. However, as distance of earth from the sun is huge `( ~~ 10^(11)m)`, portion of the wavefront on earth can be treated as plane wavefront.