Question

define the principal focus :
a. concave mirror
b. convex mirror

Answer 1

For a concave mirror. The rays traveling parallel to the principal axis of a mirror after reflection pass through (converge at) a point F This point F is known as the principal focus of the concave mirror. It is a real point in front of a mirror
.For a convex mirror. The rays traveling parallel to the principal axis of a mirror after reflection appear to diverge from a point F on the principal axis. This point F is known as the principal focus of the convex mirror. It is a virtual point, i.e., behind the mirror.

Answer 2

a)the rays parallel to principal Axis gets reflected from the mirror and meet in front of the mirror at a single. it is the focus of a concave mirror

b)when several rays of light parallel to principal Axis are incident on a convex lens they converge at a point on the principal axis. it is the principal focus of a convex mirror