Optics
White-light prism
A prism refracts blue more than red, so white light fans out into a spectrum (δ = θ₁ + θ₄ − A).
White-light prism — interactive Optics simulation. A prism refracts blue more than red, so white light fans out into a spectrum (δ = θ₁ + θ₄ − A). Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Dispersion
A prism refracts blue more than red, so white light fans out into a spectrum (δ = θ₁ + θ₄ − A).
Snell's law uses wavelength-dependent index n(λ), so each color refracts by a slightly different angle. A prism's apex separates white light into a spectrum with violet bent most. The angular dispersion δ depends on the prism angle and material Abbe number.
- n varies with λ
- Blue bends more
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
Light entering a glass prism bends (refracts) at each face, emerging deviated from its original direction. Does changing the incidence angle at the first face always change the total deviation in the same direction?
Predictions to weigh
- Deviation always increases as incidence angle increases.
- No — deviation actually has a minimum at some specific incidence angle, not a simple increasing or decreasing trend.
- Deviation always decreases as incidence angle increases.
Variable roles
What you set:
- Incidence angle θ₁ (°)
What you measure:
- Total deviation δ (°)
How the investigation runs
- Open the white-light-prism preset and press Reset. This crown-glass prism has apex angle A = 60°, index n = 1.5.
- Enable the total-deviation readout.
- Set the incidence angle at the first face for each trial and record the total deviation.
Governing equation
Prism Deviation — δ = θ₁ + θ₄ − A
A ray passing through a prism refracts at both faces. Total deviation combines both bends and the prism's own apex angle: δ = θ₁ + θ₄ − A, where θ₂ and θ₄ come from Snell's law at each face.
What the printable worksheet asks students to work out
- For one trial, compute θ₂ = asin(sin θ₁/n) (Snell at the first face), θ₃ = A − θ₂ (prism geometry), θ₄ = asin(n·sin θ₃) (Snell at the second face), then δ = θ₁ + θ₄ − A. Compare to the table.
- Explain why deviation isn't a simple monotonic function of incidence angle — the prism's geometry (bending at TWO faces) creates a genuine minimum at the angle of symmetric passage, explored directly in the min-deviation experiment.
Where this shows up beyond the lab
- White light contains many wavelengths, each with a slightly different refractive index (dispersion) — so each color deviates by a slightly different amount, fanning white light into a visible spectrum. This experiment uses a single representative index; real white light spreads into a rainbow.
- A rainbow forms from sunlight refracting and internally reflecting inside spherical raindrops — a more complex geometry than this flat-faced prism, but driven by the exact same wavelength-dependent refraction (dispersion) principle.
- AP Physics 2 — Unit 13: Geometric Optics
- General High School Physics — Light & optics
- NGSS High School Physics — Wave properties
- Welcome to White Light Prism
- Select the prism
- Press Play
- White light spreads
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.