A combination is made of two lenses of focal lengths and in contact; the dispersive…

PHYSICS · Single correct · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments

Problem

A combination is made of two lenses of focal lengths

f

and

f'

in contact; the dispersive powers of the materials of the lenses are

\omega

and

\omega'

. The combination is achromatic when: (a)

\omega = \omega_0, \omega' = 2\omega_0, f' = 2f

(b)

\omega = \omega_0, \omega' = 2\omega_0, f' = f/2

(c)

\omega = \omega_0, \omega' = 2\omega_0, f' = -f/2

(d)

\omega = \omega_0, \omega' = 2\omega_0, f' = -2f