Which one of the following spherical lenses does not exhibit dispersion? The radii of curvature of the surfaces of the lenses are as given in the diagrams. `

Options

A.
B.
C.
D.

Answer

D

Explanation

`(1)/(f) = (mu - 1)((1)/(R_(1)) - (1)/(R_(2)))`
For no dispersion, `d((1)/(f)) = 0`
`:. D mu((1)/(R_(1)) - (1)/(R_(2))) = 0, :. R_(1) = R_(2) = R`.
Choice (d) is correct.