Question

Define 1 dioptre of power of a lens.

Answer 1

1 dioptre of power:

1. 1 dioptre of lens power is defined as the unit of measurement of a lens's or curved mirror's optical power equal to the reciprocal of focal length ($f$).
2. $P=\frac{1}{f}=1D$
3. The focal length is measured in metres.
4. The SI unit of lens power is dioptre, which has a focal length of one metre and is denoted by the letter $D$.