An achromatic convergent system of focal length 20 cm is

Last updated: 6/26/2023

An achromatic convergent system of focal length 20 cm is made of the lenses in contact of materials having dispersive powers in the ratio 1 2 Their focal length must be respectively 1 10 cm 20 cm 2 20 cm 10 cm 3 10 cm 20 cm 4 20 cm 10 cm