A) 10 cm convex and 15 concave
B) 5 cm convex and 10 cm concave
C) 15 cm convex and plane
D) 20 cm convex and 30 cm concave
Correct Answer: A
Solution :
Applying the lens makers formula \[\frac{1}{f}=P=(n-1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] We know that the greater positive power is for that material for which\[\frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}}\] is maximum and positive. For this condition \[{{R}_{1}}\] and \[{{R}_{2}}\] should be small as possible but still it must be positive, therefore we must select the combination which has less radius of curvature for convex lens. Hence, option (a) is correct.
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