Critical Angle (Also seen in GCSE Physics 3)

We can derive an equation that connects the critical angle with the refractive indices of the materials.

but at the critical angle θ₂ is equal to 90° which makes sinθ₂ = 1

θ₁ is the critical angle which we represent as θ_C making the equation:

When the second material is air n₂ = 1, so the equation becomes: or