Question

What do you mean by power of a lens? Write its SI unit.

Hint:

A convex lens has positive power, while a concave lens has negative power.

Answer 1

The power of a lens (\( P \)) is defined as the reciprocal of its focal length (\( f \)) in meters:
\[ P = \frac{1}{f} \] The SI unit of power of a lens is dioptre (\( D \)), where \( 1D = 1m^{-1} \).