What is the name of the line that passes through the center of curvature and is normal to the mirror?

The line that passes through the center of curvature of a mirror and is normal (perpendicular) to the mirror's surface is called the principal axis. This line is significant in optics because it serves as a reference point for locating the focal point of the mirror and helps in understanding how light rays behave when they strike the mirror.

In concave and convex mirrors, the principal axis also aids in determining the characteristics of the image formed by the mirror. For concave mirrors, the focal point lies along this axis, while for convex mirrors, the focal point is virtual and also aligned with this line. The principal axis essentially provides a straightforward framework for studying the relationships between object placement, image characteristics, and focal points in mirror systems, making it a fundamental concept in the study of optics.