Question

What is a principal focus? Give definition.

Answer 1

A number of rays parallel to the principal axis after reflection from a concave mirror meet at a point on the principal axis or appear to come from a point after reflection from a convex mirror on the principal axis. This is called principal focus.When the object is placed beyond C.

Answer 2

principal focus, focus the point on the axis of a lens or mirror to which parallel rays of light converge or from which they appear to diverge after refraction or reflection.