A plano convex lens fits exactly in to a plano concave lens. Their plane surfaces are parallel to each other. Lenses are made up of different materials of refractive indices ' n₁ ' ' n₂ ' and ' R ' is the radius of curvature of the curved surface of lenses. Focal length of the combination is (a) (R)/(n₁ + n₂) (b) (2R)/(n₁ - n₂) (c) (R)/(2(n₁ - n₂)) (d) (R)/(n₁ - n₂)

Answer: (d). Plano-convex: P₁ = (n₁-1)/(R); plano-concave of same R: P₂ = -(n₂-1)/(R). P = P₁ + P₂ = (n₁ - n₂)/(R) So the answer is (d) (R)/(n₁ - n₂).

A plano convex lens fits exactly in to a plano concave lens. Their… | MHT CET 2025 (21 Apr, Shift 2)

Q17MHT CET 2025 · 21 APR · SHIFT 2Medium

Combination of Lenses

A plano convex lens fits exactly in to a plano concave lens. Their plane surfaces are parallel to each other. Lenses are made up of different materials of refractive indices ' $n_1$ ' ' $n_2$ ' and ' R ' is the radius of curvature of the curved surface of lenses. Focal length of the combination is

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Answer: (d)

Plano-convex: $P_1 = \frac{n_1-1}{R}$ ; plano-concave of same $R$ : $P_2 = -\frac{n_2-1}{R}$ .
$P = P_1 + P_2 = \frac{n_1 - n_2}{R}$
So the answer is (d) $\frac{R}{n_1 - n_2}$ .

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Combination of Lenses question from MHT CET 2025 (21 Apr, Shift 2)

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