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Curved surfaces of a plano-convex lens of refractive index μ₁ and a plano-concave lens of refractive index μ₂ have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses.

Asked in JEE Main 27th Aug 2nd Shift 2021 · Combinations and silvered lenses

• (1) 1/(μ₂-μ₁)
• (2) 1/(μ₁-μ₂)
• (3) μ₂-μ₁
• (4) μ₁-μ₂

Step-by-step solution

Why the other options are wrong

• (1) Gives the ratio f/R and with the sign reversed.
• (2) Gives the ratio f/R instead of R/f.
• (3) Reverses the sign by taking the concave lens as the converging one.

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