What is the critical angle for light traveling in a polystyrene (a type of plastic) pipe surrounded by air?

Strategy

The index of refraction for polystyrene is found to be 1.49 in Figure 25.14, and the index of refraction of air can be taken to be 1.00, as before. Thus, the condition that the second medium (air) has an index of refraction less than the first (plastic) is satisfied, and the equation θ_c = sin^-1 (n₂₁) can be used to find the critical angle θ_c. Here, then, n₂ = 1.00 and n₁ = 1.49.

Data from Figure 25.14