Question

Express the power (with sign) of a concave lens of
focal length 20 cm.
​

Answer 1

we know that focal length of concave lens is negative.

so,

f = -20 cm= (-20/100) m

power, p = 1/f

so, p = 1/(-20/100) = -5 dioptre

hence, power of lens is -5 dioptre.

Answer provided by GauthMath.