Question

A convex lens has mean focal length of 20 cm. The dispersive power of the material of the lens is 0.02. Then longitudinal chromatic aberration for objective at infinity is:

• A. 0.2
• B. 0.4
• C. ${10}^{-3}$
• D. ${10}^3$

Answer 1

The correct option is B 0.4

$f_1-f_2=w\times f-\text{(i)}$

$\begin{array}{c}f=20m\\ \omega =0.02\\ f_1-f_2=\text{longitudinal}\\ \text{chromatic aberration}\\ \text{On putting values in (í)}\\ \begin{array}{cc}{f}_1-f_2& =20\times 0.02\\ & =0.40\end{array}\end{array}$