Question

The power of a lens is +2.0D. Its focal length should be :
(a) 100 cm
(b) 50 cm
(c) 25 cm
(d) 40 cm

Answer 1

(b) 50 cm

Focal length = $\frac{1}{\mathrm{Power}}=\frac{1}{2.0}=0.5\mathrm{m}=50\mathrm{cm}$