Question 2

  Two slabs with parallel faces are made from different types of glass. A ray of light travels through air and enters each slab at the same angle of incidence, as the drawing shows. Which slab has the greater index of refraction? Why?

SOLUTION: When the light enters slab B, it is bent more toward the normal (that is, its angle of refraction is less) than when the light enters slab A. Snell's Law says

$$n_1 \sin\theta_1 = n_2 \sin\theta_2 .$$

So, when n₁ < n₂, the angle of refraction will be less than the angle of incidence. The larger n₂ is, the smaller the angle of refraction. We conclude, then, that slab B must have the greater index of refraction.