Question

What is the shape of the wavefront in each of the following case:

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

A)
The shape of the wavefront in case of a light diverging from a point source is spherical as it travels in all direction.
Final Answer: Spherical.

B)

The light rays emerging out of a convex lens when a point source is placed at its focus are parallel. When light rays come from infinity parallelly, they intersect at focus of convex lens and hence when light is emerging from the focus, the rays will get parallel to each other after coming out of the convex lens, because path of light rays are reversible. The shape of the wavefront is plane.
Final Answer: Plane.

C)

At a large distance from the source, a small portion of the spherical wave can be approximated to be a plane wave. Therefore, the portion of the wavefront of light from a distant star intercepted by the Earth is a plane.
Final Answer: Plane.