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Total Internal Reflection | 1 | 2 | Rutgers University Physics

2. Critical Angle θ_c– angle of incidence for which the angle of refraction equals 90⁰ when light travels inside one medium that borders on air or a vacuum

(n = 1) (fast medium)

Air (n₂ = 1)

Deriving Critical Angle Equation

n₁sinθ₁ = n₂ sinθ₂

    Substitute θ_c, θ₂ = 90, n₂ = 1

n₁sinθ₁ = 1sin90

n₁sinθ₁ = 1

 sinθc = 1/n₁

Ex) Find θc for Lucite

sin θc = 1/n₁

From reference table, n₁ = 1.50 

sinθ_c = 1/1.50

θ_c = 41.8

3. Total Internal Reflection

Total Internal Reflection - St. Mary's H.S.

These kinds of fibers are coated with materials that have a low index of refraction (fast). These materials are called cladding.

When θ₁ > θ_c
Total Internal Reflection

EXAMPLE - LUCITE

When θ₁ = θ_c , θ₂ = 90⁰

When θ < θ_c Refraction

Refraction of Light - Rick Reed

Refraction/Reflection Video - St. Mary's University 

a) Total Internal reflection?

b) Refraction?

c) Impossible?

Dispersion