Derive lens formula for a concave lens.

The lens formula is

Derive lens maker's formula for a thin convex lens.

What is a concave lens ?

Assertion:A convex lens and a concave lens are kept in contact. They will behave as a diverging lens if focal length of convex lens is more. Reason: Power of a concave lens is always less than the power of a convex lens, as power of concave lens is negative whereas power of convex lens is positive.

State used of a concave lens.

State two differences between a convex lens and a concave lens. Give one use of convex lens and one of concave lens.