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 the greatest power is:

Options

• P

• Q

• R

• S

Answer 1

 R

Explanation:

Power = `1/"focal length"` 

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