Question

A beam of light consisting of red, green and blue colours is incident on a right-angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are $1.39$ , $1.44$ and $1.47$ respectively.

The prism will:

• A. Separate all the three colours from one another
• B. Not separate the three colours at all
• C. Separate the red colour part from the green and blue colours
• D. Separate the blue colour part from the red and green colours

Answer 1

Answer: (C)

​
For Total internal reflection, $i>i_{c}$
so, $sini>sinI_{c}$
$sin45^{o}>\frac{1}{\mu }\Rightarrow \mu =\sqrt{2}\Rightarrow \mu =1.414$
Since $\mu $ of green and violet is greater than $1.414$ , so they will undergo total internal reflection. But red colour will be refracted. So the prism will separate red colour from the green and blue colours.