Question

The power of a lens being +4 dioptres suggests that it is a ______.

Options

• convex lens

• plano-convex lens

• concave lens

• none of these.

Answer 1

The power of a lens being +4 dioptres suggests that it is a convex lens. 

Explanation: 

A convex lens has a positive focal length, and hence its power is positive ($$+4\text{ D}$$). A concave lens always has a negative focal length and negative power.