• question_answer The power of an achromatic convergent lens of two lenses is$+2D$. The power of convex lens is$+5D$. The ratio of dispersive power of convex and concave lens will be :- A)  $5:3~$B)  $3:5$C)  $\text{2}:5$               D)  $5:2$

${{P}_{1}}+{{P}_{2}}=2D$ and ${{P}_{1}}=5D$, so ${{P}_{2}}=-3D$ For achromatic combination $\frac{{{\omega }_{1}}}{{{\omega }_{2}}}=\left( -\frac{{{P}_{2}}}{{{P}_{1}}} \right)=\left( \frac{-3}{5} \right)=\frac{3}{5}$