An achromatic lens-doublet is formed by placing in contact a convex lens of focal length
Channel: Doubtnut
Date: 2020-07-05

An achromatic lens-doublet is formed by placing in contact a convex lens of focal length `20 cm` and a concave lens of focal length `30 cm.` The dispersive power of the material of the convex lens is `0.8.`  Determine the dispersive power of the material of the concave lens.  Calculate the focal length of the lens-doublet.