Question

The colour which has least critical angle is

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

Answer 1

Answer: (C)

Violet

$\begin{array}{c}\text{For total internal reflection to take place.}\\ \begin{array}{c}\mu \sin {\theta }_c=1\\ {\theta }_c={\sin }^{-1}\left(\frac{1}{\mu }\right)\end{array}\end{array}$

$\begin{array}{c}\text{As a fact, the refractive index for a ray is inversely}\\ \text{proportional to its wavelength.}\end{array}$

$\begin{array}{c}\mu \times \frac{1}{\lambda }\\ \text{Since violet has shortest wavelength it's critical}\\ \text{angle is also low}\end{array}$