Question

Refractive index of violet, yellow and red color of light for a material of lens are $1.66,1.64$ and $1.62$ respectively. If mean focal length of lens is $10\text{cm}$. Then chromatic aberration between the color of viole and red will be

• A. $0.625\text{cm}$
• B. $0.125\text{cm}$
• C. $0.02\text{cm}$
• D. $0.025\text{cm}$

Answer 1

The correct option is A $0.625\text{cm}$

Dispersive power $\omega =\frac{n_y-n_R}{n_y-1}$
$=\frac{1.66-1.62}{1.64-1}=\frac{0.04}{0.64}=\frac{1}{16}$

Now chromatic aberration between violet and red $(f_y-f_R)=df$
$\Rightarrow df=\omega f=\frac{1}{16}\times 10=\frac{5}{8}=0.625\text{cm}$