Question

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.

Answer 1

(a) The geometrical shape of the wave front would be diverging spherical wave front, as shown in Fig.
(b) When point source is placed at the focus of a convex lens, the rays emerging from the lens are parallel. Therefore, the wave front must be plane, as the shown in Fig.
( c) As the star (i.e. source of light) is very far off i.e. at infinity, the wave front intercepted by earth must be a plane wave front as shown in Fig.