Critical Angle (Total Internal Reflection)
Critical Angle (Total Internal Reflection)
Above the critical angle, light striking a boundary to a less dense medium reflects entirely — the trick that guides light in optical fibres.
The critical angle is θ_c = arcsin(n_2/n_1). where n_1 is the denser medium’s index and n_2 the lighter medium’s.
Inputs
n_1 := 1.5=1.5
n_2 := 1.0=1
Apply the critical-angle formula.
theta_c := asin(n_2/n_1)=0.73 rad
Results
For glass-to-air the critical angle is about 42° (0.73 rad). Rays striking more steeply than this are trapped, carrying signals along a fibre.
Assumptions & limitations
- Light going from denser to lighter medium.
- Angles from the normal.
- Result in radians.