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MHT CET 2021 (23 Sep, Shift 2) · Combination of Lenses

Combination of Lenses question from MHT CET 2021 (23 Sep, Shift 2)

Q46MHT CET 2021 · 23 SEP · SHIFT 2Medium

Combination of Lenses

A plano-convex lens of refractive index ( $\mu_1$ fits exactly into a plano-concave lens of refractive index $\mu_2$ . Their plane surface are parallel to each other. 'R' is the radius of curvature of the curved surface of the lenses. The focal length of the combination is

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Answer: (a)

Plano-convex: $P_1 = \frac{\mu_1-1}{R}$ ; plano-concave of same $R$ : $P_2 = -\frac{\mu_2-1}{R}$ .
$P = P_1 + P_2 = \frac{\mu_1 - \mu_2}{R}$
So the answer is (a) $\frac{R}{\mu_1 - \mu_2}$ .

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