Physics - Geometrical Optics Question with Solution | TestHub

An achromatic doublet of focal length 90cm is to be made of two lens. The material of one having 1.5 times the dispersive power of the other. The doublet is converging type. If magnitude of focal length of the lens used are ${\mathrm{f}}_1$ and ${\mathrm{f}}_2$. Find ${\mathrm{f}}_1+{\mathrm{f}}_2$ (in cm).