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 the red colour part from the green and blue colours
• B. separate the blue colour part front the red and green colours
• C. separateall all three colours from one another
• D. not separate the three colours at all

Answer 1

The correct option is A separate the red colour part from the green and blue colours

For total internal reflection, $i>i_c$
Here $i={45}^0$
$\frac{\sin i}{\sin r}=\mu$
$\sin {45}^0>\frac{1}{\mu }$
$\mu >\frac{1}{\sqrt{2}}=1.414$
${\mu }_{red}<1.414$ but ${\mu }_{green}>1.414$ and ${\mu }_{violet}>1.414$.
Hence, green and violet will be totally internally reflected.
Red will be refracted.