An achromatic convergent doublet has power of +2D. If power of convex lens is +5D, then ratio of the dispersive powers of a convergent and divergent lenses will be
Answer & explanation
Correct answer: option 1
$P=+2 D \quad ∴ P_1=+5 D \quad ∴ P_2=-3 D$
As $\frac{P_2}{P_1}=\frac{f_1}{f_2}=-\frac{w_1}{w_2}=-\frac{3}{5} \Rightarrow \frac{w_1}{w_2}=\frac{3}{5}$