Question

What type of wavefront will emerge from a
A. Point source
B. Distant light source

Answer 1

Hint: Wavefront is an imaginary surface that represents the locus of all the points in an optical field having the same phase at a given instant.

General properties of a wavefront are:
A wavefront is dependent on the shape of the source of disturbance
A wavefront does not travel backwards.
A wavefront is normal to the light rays.
Types of wavefronts:
Spherical wavefront: Very similar to ripples in water, this wavefront is produced by a point source.
Plane wavefront: Rays coming from a distant source generate a plane wavefront.
Cylindrical wavefront: When the light rays converge or diverge from a lens a cylindrical wavefront is formed.

Complete step by step solution:
Point source is that source which is so small that it is considered as a single point. Such sources are dimensionless.
The wavefront emerging from a point source is the spherical wavefront since the waves travel radially outwards from the source.
Hence the wavefront for a point source is spherical.

A distant source is so far away that it is considered to be at infinity, the rays travelling from a distant light source are taken as planes moving in the direction of propagation of waves. And hence the wavefront is a plane wavefront.

Hence the wavefront emerging from a distant source is a plane wavefront.

Note:
Wavefront is the locus of all the points in the field which have the same phase at a given instant. This means that even if the phase is the same at different points in time, the two points may or may not be considered as a part of the wavefront. Also, we must keep in mind that the direction of propagation of the wavefront is the direction of propagation of the wave.