Question

Focal lenghts of two lenses are $10\text{cm}$ and $-20\text{cm}$ and dispersive powers of their materials are $0.03$ and $\omega$ respectively. To form a chromatic combination from these, the value of $\omega$ is

• A. $0.02$
• B. $0.04$
• C. $0.06$
• D. $0.08$

Answer 1

The correct option is C $0.06$

We know that the condition of achromatic is
$\frac{{\omega }_1}{f_1}+\frac{{\omega }_2}{f_2}=0$
$\Rightarrow \frac{0.03}{10}+\frac{\omega }{(-20)}=0$
$\Rightarrow \omega =0.06$