Exercise 10.2 Physics 12. What is the shape of the wavefront in each of the following cases

ITT, JEEE, NCERT Exercise 10.2 Physics Class 12,
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.