The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

What is centre of curvature of a spherical mirror?

What is pole of a spherical mirror?

An object is at a distance of 1 metre from the pole of a concave mirror. Its image is found to be one-third of the size of the object. Find the position of the image, radius of curvature of the mirror and its focal length.

A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.