NCERT · Class 10 · Science · Light – Reflection and RefractionState the relationship between the radius of curvature and the focal length of a spherical mirror.

For any spherical mirror, whether concave or convex, of small aperture, the radius of curvature is found to be exactly twice its focal length. Mathematically, this relationship is expressed by the standard formula R equals 2f, or equivalently, f equals R divided by 2. This implies that the principal focus lies precisely at the midpoint of the straight line segment joining the pole of the mirror and its center of curvature. This fundamental geometric property is extensively used in mirror formula calculations.