Question

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.

Answer 1

The geometrical shape of the wave front in case of light diverging from a point source will be diverging spherical wavefront.

When a point source is placed at the focus of convex lens,the rays emerging from the line are prallel.

The source of light (i.e. star) is very far off (i.e. at infinity) the wavefront intercepted by the earth will be a plane wavefront

Answer 2

a) Spherical wave front : All particles vibrating in same phase will lie on a sphere.

(b) Plane wave front: Light will be a parallel beam after passing through the convex lens.

(c) Plane wave front : Light rays from a distant star are nearly parallel as a small portion of a huge spherical wave front is nearly plane.