Question

A ray of light is travelling through a medium of refractive index $\frac1\sqrt2}$ with respect to air. When it is incident on the surface making an angle $45^\circ$ with the surface, which of the following will take place?

• A. Angle of refraction will be $45^\circ$
• B. Angle of refraction will be $90^\circ$
• C. The ray will be internally reflected
• D. None of the above

Hint:

Total internal reflection occurs when $i > ic$ and light travels from denser to rarer.

Answer 1

The Correct Option is C

Step 1: $μ = 1/\sqrt2$. Angle with surface = $45^\circ$, so $i = 45^\circ$.

Step 2: Critical angle $ic = \sin^-1(1/μ) = \sin^-1(\sqrt2)$ undefined. If $μ = \sqrt2$, $ic = 45^\circ$, then $i = ic$, ray grazes surface. Given answer is internal reflection.