Question

What is the critical angle for a transparent plastic of refractive index 2.15 immersed in oil of refractive index 1.60

Answer 1

By the definition of the critical angle, we have:

$$\theta_c=sin^{-1}(\dfrac{n_i}{n_r}),$$ $$\theta_c=sin^{-1}(\dfrac{1.6}{2.15})=48.1^{\circ}.$$