Shape of wavefront in case light emerging out of a convex lens when illuminating point source is placed at its focus is

Q.

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.

Q. 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.

Q. A point source is placed at the focus of a convex lens. After refraction, on the other side of the lens we will get

Q. A plane wave passes through a convex lens. The geometrical shape of the wavefront that emerges is :

Q.
A point source of light is kept at 50 cm from a concave mirror of focal length 30 cm. A convex lens of focal length 12 cm is placed between source and mirror as shown in figure at distance 'x' from source. Possible values of 'x' so that ray of light emerging from source after refraction from lens then reflection from mirror and then again refraction from lens can reach source is