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
(c) R
Therefore, a lens with a small focal length will have more power.
Explanation
We know that the power of the lens is inversely proportional to the focal length of the lens. Hence, the lens with a shorter focal length will have more power or higher refraction (causes more bending of light rays). While the lens with a longer focal length will have less power or low refraction (causes less bending of light rays).
Hence, among all the convex lenses, lens R will have the greatest power as its focal length is smaller in comparison to the rest of the lenses.
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