Question

What is the shape of the wavefront in each of the following cases?

i. Light diverging from a point source.

ii. Light emerging out of a convex lens whenapointsource isplaced at its focus.

iii. The portion of the wavefront of light from a distant star intercepted by the earth.

Answer 1

i. The geometrical shape of the wavefront for the light diverging from a point source would be diverging spherical wavefront, as shown in figure (a).

ii. For a point source placed at the focus of a convex lens, the rays emerging from the lens are parallel. Hence the wavefront is a plane wavefront as shown in figure (b).

iii. As the star (i.e. source of light) is very far i.e. at infinity, the wavefront of the light coming from it which is intercepted by earth is a plane wavefront as shown in figure (b).