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

C

Explanation

`(1)/(f) = (mu -1) ((1)/(R_(1)) - (1)/(R_(2)))`
For no dispersion
`d{(1)/(f)} = 0 implies "d"mu{(1)/(R_(1)) - (1)/(R_(2))} = 0 implies R_(1) = R_(2)`