An achromatic convergent doublet of two lenses in contact has a power of + 2D. The convex lens has a power + 5D. What is the ratio of the dispersive powers of the convergent and divergent lenses
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Question

An achromatic convergent doublet of two lenses in contact has a power of + 2D. The convex lens has a power + 5D. What is the ratio of the dispersive powers of the convergent and divergent lenses

G1 Physics · Accepted Answer

Derived solution: Step 1: For thin prisms/lenses use dispersion relations. For an achromatic doublet, ω₁P₁ + ω₂P₂ = 0, while the net power is P₁ + P₂. Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 3 : 5. Therefore the correct option is B.