Question

Calculate the focal length of one of the thin lenses if the resultant focal length is $5\text{cm}$, and one lens has a focal length $10\text{cm}$ used to minimize the chromatic aberration.

• A. $20\text{cm}$
• B. $15\text{cm}$
• C. $10\text{cm}$
• D. $30\text{cm}$

Answer 1

The correct option is C $10\text{cm}$

Given : $f_{eq}=5\text{cm},f_1=10\text{cm},f_2=?$
So using,
$\frac{1}{f_2}=\frac{1}{f_{eq}}-\frac{1}{f_1}$
$\frac{1}{f_2}=\frac{1}{5}-\frac{1}{10}=0.1$
$f_2=10\text{cm}$
So, the second lens has a focal length of $10\text{cm}$ which leads to reduction of a chromatic aberration.