Question

Define the following terms in reference to spherical mirror: pole, principal axis, focus, focal length, centre of curvature and radius of curvature.

Answer 1

A spherical mirror is a mirror that has the shape of a piece cut out of a spherical surface.

The two types of spherical mirrors are:

1. Concave mirror
2. Convex mirror

1. Pole: The centre of reflecting surface. It is represented by letter P.
2. Principal axis: The straight line joining the pole (P) and the centre of curvature. It is normal to the mirror at its pole.
3. Focus: The point of principal axis at which the rays parallel to the principal axis meet (concave mirror) or appear to meet (convex mirror) after reflection. Represented by F.
4. Focal Length: The distance between the pole and the principal focus of a spherical mirror is called focal length. Represented by f.
5. Centre of Curvature: The centre of the sphere of which the mirror forms the part. Represented by C.
6. Radius of Curvature: The radius of the sphere of which the mirror forms the part. Represented by R.