Question

A ray of light travelling in 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 TIR?

• A. $\mu >1.33$
• B. $\mu >1.4$
• C. $\mu >1.2$
• D. $\mu >1.25$

Answer 1

The correct option is B $\mu >1.4$

Condition for TIR
$i\ge C$
$sini\ge sinC$ ....(1)
$sinC=\frac{1}{\mu }$ use equation (1)
$sini\ge \frac{1}{\mu }\mu \ge \sqrt{2}\Rightarrow \mu \ge 1.412$