Question

Define the principal focus of a spherical mirror.

Answer 1

Explanation,

1. A spherical mirror is a mirror that has the appearance of a spherical surface cut out of a portion.
2. Two kinds of spherical mirrors are available: concave and convex mirrors.
3. The principal focus or focal Point of a spherical mirror is on the axis of a mirror or lens where after reflection or refraction rays of light parallel to the axis converge or begin to converge.
4. If a bunch of rays of light is shined straight at a concave mirror, all of those beams will be mirrored by the mirror and will all meet at one point. That point is called the principal focus or focal point.
5. In the figure below $F$ is the principal focus.