Question

An achromatic convergent doublet of two lenses in contact
has a power of + 2D. The convex lens has power + 5D. What
is the ratio of dispersive powers of convergent and divergent
lenses ?
(a) 2 : 5 (b) 3 : 5 (c) 5 : 2 (d) 5 : 3

Answer 1

Goven: P1 = 5 D P - 2 = P - P1 = 2 - 5 = - 3D ω1/ω2 = - f1/f2 = - P_2/P1 = 3/5

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Answer 2

Answer:

    B

Explanation:

achromatic convergent doublet

P1 +P2 = P

5 + P2 = 2

P2 = -3

W1P1 +W2P2 = 0

W1P1 = - W2P2

W1/W2 =  -P2/P1

            =  3/5