Question

The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S

Answer 1

 R

Power=`1/"focal length"` 

Therefore, a lens with a small focal length will have more power.