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प्रश्न
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
उत्तर
R
Power=`1/"focal length"`
Therefore, a lens with a small focal length will have more power.
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