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  4. The deviation is maximum for which colour?

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Q. The deviation is maximum for which colour?

Rajasthan PMTRajasthan PMT 2007Ray Optics and Optical Instruments

Solution:

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