Question

For which of the given colours, Critical angle of light passing from glass to air is minimum.

[Assume, reflection at interface is negligible]

• A. red
• B. green
• C. yellow
• D. violet

Answer 1

The correct option is D violet

We know that,

For a glass-air interface,

$\sin {\theta }_c=\frac{1}{\mu }$
or, ${\theta }_c={\sin }^{-1}\left(\frac{1}{\mu }\right)$

From the equation we can conclude that :
As the value of $\mu$ is maximum for the violet light, the critical angle will be minimum $($Least$)$ for the violet light.

Hence, option (d) is the correct answer.

Why this question? Note:- At an interface, critical angle varies with wavelength of incident light.