What is the difference between a convex lens and concave lens?

Why a convex lens called converging Iens?

Eye lens is

What is the lens in eye?

Explain why a convex lens is called a converging lens.

If the refractive index of convex lens and surrounding medium be mu_1 and mu_2 respectively then for convex lens to act as concave lens when

What is meant by the optical centre of a convex lens?