A point source of light is placed at the principal focus of a convex lens. The light emerging from the lens falls on a concave mirror placed coaxially. The shape of the wavefront reflected by the concave mirror is :

Step-by-step solution

Light rays originating from a point source at the focus of a convex lens emerge parallel to the principal axis. These parallel rays correspond to an intermediate plane wavefront. When these parallel rays strike the concave mirror, they are reflected such that they converge towards the focus of the mirror. Since the reflected rays are converging to a point, the corresponding wavefront perpendicular to these rays is spherical. Answer: spherical