Question

A ray of light travelling in a transparent medium of refractive index $\mu$, falls on a surface separating the medium from air at an angle of incidence of $45^{\circ}$. For which of the following value of $\mu$ the ray can undergo total internal reflection?

• A. $\mu =1.33$
• B. $\mu =1.40$
• C. $\mu =1.50$
• D. $\mu =1.25$

Answer 1

Answer: (C)

For total internal reflection, $\sin i >\sin c$ where, $i =$ angle of incidence, $C =$ critical angle
But, $\sin C =\frac{1}{\mu} \therefore \sin i =\frac{1}{\mu}$ or $\mu=\frac{1}{\sin i }$
$ \left.\therefore \mu>\frac{1}{\sin 45} \text { or } \mu>\sqrt{2} \text { (i = } 45 \text { Given }\right) $