Question

A ray of light travelling in a transparent medium of refractive index falls on a surface separating the medium from the air at an angle of incidence of 45. For which of the following values of the ray can undergo total internal reflection?

• A. 1.5
• B. 1.41
• C. 1.33
• D. 1.75

Answer 1

The correct option is B 1.41

We know, the refractive index of air is $1,$ Let the refractive index of medium be $\eta$

The angle of incidence is given as ${45}^0$

For total internal reflection, the angle of refraction must be ${90}^0$

For total internal reflection, $\eta \times sin45\ge 1\times sin90$

$\Rightarrow n\ge \sqrt{2}$

$\Rightarrow n\ge 1.414$

So the possible value of $\eta$ is $1.5,$

Therefore the correct option is $B.$