Prism dispersion and refraction simulation

A prism splits white light because glass bends different colours by different amounts. Violet light slows down more in glass than red light, so it refracts more at each surface and the colours fan out.

Interactive, free and runs in your browser. Part of the Optics simulations.

What you will see

Forty-eight wavelengths from violet to red enter a glass prism together and leave as a spectrum on the screen, using Cauchy’s dispersion formula for the refractive index. Steepen the prism and some rays hit the far face beyond the critical angle and reflect back inside instead of escaping.

Try this

  1. Compare the deviation of the violet and red rays.
  2. Increase the prism angle until the first colour undergoes total internal reflection.
  3. Watch which colour disappears first, and explain why.

Common misconception

The prism does not add colour to white light. White light already contains all the colours; the prism only separates them because each one refracts by a different amount.

Exam-style question

What is the critical angle for light going from glass (n = 1.50) into air?

sin θ_c = 1/n = 1/1.50 = 0.667, so θ_c ≈ 41.8°. Rays meeting the glass–air surface at more than 41.8° to the normal are totally internally reflected.

Key equations

  • n₁ sin θ₁ = n₂ sin θ₂
  • sin θ_c = n₂ / n₁
  • n(λ) = A + B / λ²

Curriculum

AQA A-level physics 3.3.2, IB Physics C.2 and C.3.

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