Two lens in contact form an achromatic combination. Their focal lengths are in the ratio of 2 : 3. Their dispersive powers will be in the ratio of :
(a) 3 : 1
(b) 1 : 3
(c) 2 : 3
(d) 3 : 2
Correct option (c) 2 : 3
Explanation:
The condition for the achromatism is given by
