Question

The dispersive powers of the materials of the two
lenses are in the ratio 4: 3. If the achromatic
combination of these two lenses in contact is a
convex lens of focal length 60 cm then the focal
lengths of the component lenses are
(1) - 20 cm and 25 cm
(2) 20 cm and - 25 cm
(3) - 15 cm and 40 cm
(4) 15 cm and - 20 cm​

Answer 1

Answer:

Option (2)

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