Question

The deviation is maximum for which colour?

• A. Violet
• B. Red
• C. Blue
• D. Green

Answer 1

Answer: (A)

We know that wavelength of violet light is minimum and that of red light is maximum.
$\therefore {\lambda }_R>{\lambda }_V$
From Cauchy's dispersion relation
$\mu \propto \frac{1}{\lambda }$
So, ${\mu }_V>{\mu }_R$, ie, refractive index of glass for violet light is maximum.
Hence, from the formula

${\delta }_m=(\mu -1)A$
where ${\delta }_m$ is angle of deviation and $A$ the angle of prism, violet light deviates the most and red the least.