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Ratio of dispersive powers of the lenses of an achromatic doublet of power +2 D with a +5 D convex lens

The same question, asked 2 times: 20 Apr 2025 S2, 15 May 2026 S1. Every wording below, oldest first.

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  1. Question 1

    20 Apr 2025 S2

    31
    An achromatic convergent doublet of two lenses in contact has a power +2 D . The convex lens has power + 5D. The ratio of the dispersive powers of the convergent and divergent lenses is (in magnitude)

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  2. Question 2

    15 May 2026 S1

    140
    An achromatic convergent doublet of two lenses in contact has a power of +2D+2D. The convex lens has power +5D+5D. What is the ratio of the dispersive powers of the convergent and divergent lenses?

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