Important terms Related to Spherical Mirrors :
- Aperture : An Aperture of a spherical mirror gives the size of the mirror. MN is the Aperture of the Mirror.
- Pole : The centre of the spherical surface of the mirror is known as the pole of the mirror. It lies on the surface of the mirror . In the diagram , P is the pole the mirror.
- Centre of curvature: it is the centre of the hollow sphere of glass of which the mirror is a part. The centre of curvature of a concave mirror is the front of it but the centre of curvature of a convex mirror is behind it. Every point on mirror surface lies at the same distance from it. Here , C is the centre of curvature of the mirror.
- Radius of curvature: The radius of curvature of a spherical mirror is the radius of the hollow sphere of the glass Or the distance between the pole of the mirror and the centre of curvature, is known as the radius of curvature of the mirror. Radius of curvature is equal to the radius of the spherical shell of which the mirror is a part. Here , PC is the radius of curvature of the mirror . It is represented by the symbol R.
- Principal axis - the straight line joining the pole of the mirror and the centre of curvature is known as the principal axis of the mirror.
- Principal focus - Principal focus is a point on the principal axis of the mirror , such that the rays incident on the mirror parallel to the principal axis , after reflection meet at this point ( in case of a concave mirror ) or appear to emerge from this point ( in case of a concave Mirror). F is the principal focus of the mirror.
- Focal length - Focal length is the distance between the pole and principal focus of the mirror. PF is the focal length of the mirror. It is represented by the symbol f . For convex f= +R/2 , for concave mirror f = -R/2. Concave has real Focus and convex mirror has virtual focus.
A plane mirror neither converges parallel rays of light not diverges them . The focal length of a plane mirror can be considered to be 'infinite' or 'infinity'.