Question

Determine the focal length of a thin converging lens if the power is 5.0 dioptres

Answer 1

Optical power of a lens is given by formula

$P = \frac{1}{f},$ where f is the focal length.

Reciprocally,

$f = \frac{1}{P} = \frac{1}{5.0\text{ dpt}} = 0.2\text{ m} = 20\text{ cm}.$