What is the distance between the pole and the principal focus of a spherical mirror called?

When light rays parallel to the principal axis fall on a convex lens,they refract and converge at a point on the principal axis. What is this point called?

How can you distinguish between a plane mirror,a convex mirror,and a concave mirror by merely looking at the image formed in each case?

At what position should an object be placed in front of a concave mirror to obtain a magnification of $(- 2)$?

Does the magnification equation change depending on whether the lens is a concave lens or a convex lens?

The figure below shows the refraction and emergence of a ray of light incident on a rectangular glass slab. Copy the diagram and mark the lateral displacement of the incident ray. Name the two factors on which the lateral displacement depends.