Question

What is a necessary condition for total internal reflection in a medium?

Answer 1

Answer:

B. when the angle of incidence is greater than the critical angle

Explanation:

As we know by law of refraction of light that

$\mu_1sin i = \mu_2 sin r$

now here we know that total internal reflection only occurs when light travel from denser medium to rarer medium.

so here

$\mu_2 < \mu_1$

now if angle is critical angle then at that point angle of refraction must be 90 degree

$sin i = \frac{\mu_2}{\mu_1}$

so if angle is more than critical angle then it will always follow the law of reflection so correct answer is

B. when the angle of incidence is greater than the critical angle

Answer 2

The correct answer is B.