Question

If the critical angle for TIR from medium to vacuum is ${30}^{\circ },$ the velocity of light in medium is:

• A. $3\times {10}^{8}m/s$
• B. $1.5\times {10}^{8}m/s$
• C. $6\times {10}^{8}m/s$
• D. $\sqrt{3}\times {10}^{8}m/s$

Answer 1

The correct option is B

$1.5\times {10}^{8}m/s$

Critical angle $C={30}^{\circ }$
$\mu =\frac{1}{sinC}=\frac{1}{sin{30}^{\circ }}\mu =2V_1=\frac{C\left(speedoflight\right)}{\mu }{V}_1=\frac{3\times {10}^8}{2}{V}_1=1.5\times {10}^{8}m/s$