Question

The refractive index of a converging lens is measured for violet, green and red colours produced by same source of light, and found to be ${\mu }_v,{\mu }_g,{\mu }_r$ respectively. The correct relation between the refractive index is:

• A. ${\mu }_r>{\mu }_g>{\mu }_v$
• B. ${\mu }_r<{\mu }_g<{\mu }_v$
• C. ${\mu }_r>{\mu }_g<{\mu }_v$
• D. ${\mu }_r<{\mu }_g>{\mu }_v$

Answer 1

The correct option is A ${\mu }_r>{\mu }_g>{\mu }_v$

A converging lens with greater refractive index $\left(\mu \right)$ will bend light rays closer to the optical centre, because refractive index of a media is directly related to its ability of bending the light rays passing through it.


We know,
$\mu =\frac{c}{v}=\frac{c}{f\lambda }$
The frequency of light is same for all, as source is same for them.
$\mu \propto \frac{1}{\lambda }$
$(\because {\lambda }_r>{\lambda }_g>{\lambda }_v)$

$\Rightarrow {\mu }_r<{\mu }_g<{\mu }_v$