Following are three main differences between spherical and plane mirrors:
1. A plane mirror has only one kind of reflecting surface which is the plane surface. A spherical mirror has two types of reflecting surface: concave surface and convex surface.
2. The radius of curvature of a plane mirror is at infinity. The radius of curvature of spherical mirror has a finite length.
3. The image produced by a plane mirror is always virtual. The image produced by a concave reflecting surface can be real as well as virtual.