Question

________ is the geometric center of a spherical mirror.
A) Principal force (F)
B) Center of curvature ( C )
C) Pole (P)
D) Secondary focus (${{F}_{2}}$ )

Answer 1

Be thorough with the above options definitions in order to solve this question. Center of curvature is a term related to curvature of mirrors and lenses. Primary and secondary focus are the terms related to lenses. Pole is the term related to mirrors, therefore it can be the correct option.

Complete step by step solution:
Let’s look what each of the options actually mean and when they are used. All these options are related to focus, where either the object is placed or the image is formed. It is possible to get confused between these terms.

Principal Focus: The first option is a misprint, instead of principal force it should have been principal focus. Let’s see whether principal focus can be the correct option. First let us know what focus means, focus is the point where light rays originating from a source converge. The point where a beam parallel to the principal axis appears to converge from a point on the principal axis after passing through the lens is called principal focus.
Clearly this term is related to lenses hence (A) is not the correct option.

Center of curvature:Center of curvature is the point on the normal at a given point on a curve on the concave side of the curve whose distance from the point on the curve is equal to the radius of curvature.
Center of curvature is related to surfaces, mirrors which are curves in shape.
Hence, option B is also correct.

Pole: Pole is the point inside the spherical mirror which is the geometrical center.The principal axis is an imaginary line passing through the optical center and center of curvature for any lens or spherical mirror.
Hence, option C is the correct option.

Note: Don’t confuse between these terms, they all are related to mirrors and lenses.
When we talk about the curvature of a mirror, then the curves are assumed to be part of some spherical mirror. Basically there are two types of mirrors: Concave mirror and convex mirror.