Light leaving a dense material for a less dense one bends away from the normal. Past a certain angle, the critical angle, it cannot leave at all and reflects entirely back inside. That critical angle is where the sine equals one over the refractive index, so a higher index gives a smaller critical angle. Raise the angle to find where the ray can no longer escape.
MissionFind the critical angle for glass.Round 1Streak 0Best 0
Above the critical angle, the light is:
materialglass (n = 1.50)
angle of incidence inside30°
critical angle (sin c = 1 ÷ n)41.8°
staterefracting out
below the critical angle light escapes; above it, total internal reflection.