The Critical Angle

• Total internal reflection occurs when the angle of incidence exceeds the critical angle, which depends on the refractive indexes of the two media.
• When the angle of incidence is equal to the critical angle, the light ray refracts along the boundary between the 2 media.
• The critical angle can be calculated using Snell's law (n1 sinθ1 = n2 sinθ2).
• When the angle of incidence is greater than the critical angle, the light ray is reflected back into the same medium.
• critical angle = sin-1(n2/n1) where n1 > n2