Question

find out the power of a convex lens having focal length of 20cm

Answer 1

$p = \frac{1}{f} \\ p = \frac{1}{ \frac{20}{100} } = \frac{100}{20} = + 5dioptre$

Answer 2

Given:-

f= 20 cm = 0.2m

W.k.that

Power = 1/ f

= 1/0.2

= +5 ans.