Question

If the focal length of a concave lens is 25 cm, find the power of the lens.

Answer 1

Given:

f = 25 cm for a concave lens → f = −25 cm = −0.25 m.

P = `1/f`

= `1/(−0.25)`

= −4 dioptres (D)

The power of a concave lens with a focal length of 25 cm is −4.