Calculate the critical angle between acrylic (n = 1.49) and water (n = 1.33).

Answer 1

Using the law of refraction (Snell's law):

n₁*sin(θ_i) = n₂*sin(θ_r),

with n₁ the index of refraction of the first medium where the incident light ray makes an angle θ_i with the perpendicular to the surface boundary.

n₂ the the index of refraction of the second medium and θ_r the angle of refraction.

The critical angle θ_c is the angle of incidence where θ_r becomes 90°.

(Larger angles of incidence gives total internal reflection).

Knowing that sin(90°) = 1, Snell's equation becomes:

n₁*sin(θ_c) = n₂

Solving for θ_c = sin^-1(n₂/n₁)

You'll find your answer with n₁ = 1.49 and n₂ = 1.33