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>>Combination of Lenses
>> $Two plano convex lenses of same material$

Question

Two plano convex lenses of same material and of focal lengths 20 cm & 5 cm should be arranged such that the combination is free from chromatic aberration. Then effective focal length of the combination will be:

A

20 cm

B

4 cm

C

12.5 cm

D

8 cm

Medium

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Updated on : 2022-09-05

Solution

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Correct option is C)

The effective focal length of the lens is,

$\frac{1}{f} = \frac{1}{f _{1}} + \frac{1}{f _{2}} - \frac{f _{1} + f _{2}}{2 f _{1} f _{2}}$

Substituting the respective values, the effective focal length obtained is, $f = 12.5$

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