The principal axis is a straight line passing through the pole and the center of curvature of a spherical mirror. It is normal to the mirror at its pole.
How is the principal axis of a spherical mirror defined, and what is its relationship to the mirror’s pole and center of curvature?
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The principal axis of a spherical mirror is an imaginary line passing through the pole (the central point on the mirror’s surface) and the center of curvature (the center of the sphere from which the mirror is derived). It is perpendicular to the mirror’s surface at the pole. In a concave mirror, the principal axis extends from the mirror, through the pole, and continues beyond the mirror. In a convex mirror, the principal axis also extends from the mirror through the pole, but it is extended behind the mirror. Understanding the principal axis is essential for analyzing image formation and optical properties in spherical mirrors.