Question

the power of lense with focal length 20 cm

Answer 1

f=20 cm
power= 100/f(in cm).
>P=100/20
>P= 5D (ans).

Answer 2

We know that power, P = 1/f

= 1/20

= 0.05D

If the P= +ve Convex

P= -ve Concave