PYQ NEET- Total Internal Reflection

• NEET 2019:

A ray of light strikes a glass slab at an angle of incidence of 60°. If the angle of refraction is 45°, the value of the critical angle for the glass slab cannot be determined from this information alone

Answer:

The critical angle is the angle of incidence for which the angle of refraction is 90°.

Explanation:

The formula for the angle of refraction is given by Snell’s Law: $ n_1 \sin(\theta_1) = n_2 \sin(\theta_2) $, where $ n $ represents the refractive index and $ \theta $ represents the angle of incidence or refraction.

sin(r) = n * sin(i)

where r is the angle of refraction, i is the angle of incidence, and n is the refractive index of the second medium.

In this case, we have r = 45°, i = 60°, and n = ?.

Plugging these values into the formula, we get:

sin(45°) = sin(60°) * n

1 / sqrt(2) = n * sqrt(3) / 2

n = 2 / sqrt(3)