Question

Define principal focus of a spherical mirror.

Answer 1

PRINCIPAL FOCUS :-

1. When rays of light traveling parallel to the principal axis of a concave mirror get reflected from it, they all pass through a common point on the principal axis after reflection.
2. This point is known as the principal focus of the concave mirror
3. For a convex mirror, the rays appear, after reflection, to come from a point on its principal axis.
4. This point is again called the principal focus of the convex mirror.
5. It means that the rays traveling parallel to the principal axis of a mirror, after reflection from it, either converge to or appear to diverge from a point on the principal axis.
6. This point is, therefore, the principal focus of the mirror.