Question

When ray of light enters from one medium to another its velocity in second medium becomes double. the maximum value of angle of incidence so that total internal reflection may not take place will be

• A. ${60}^{\circ }$
• B. ${180}^{\circ }$
• C. ${90}^{\circ }$
• D. ${30}^{\circ }$

Answer 1

The correct option is D ${30}^{\circ }$

Velocity becomes double so ${\mu }_r=2$

critical angle is $si{n}^{-1}\frac{1}{{\mu }_r}=si{n}^{-1}\frac{1}{2}={30}^{\circ }$.