Physics · Optics

Dispersion / Refractive Index and Color

Simulation loading

Open Model Lab is preparing the live lab, controls, and graph surface for this concept.

Wrap-up

What you learned

Recommended next: Open concept testCheck whether the core ideas are ready without leaving this concept.
Read next: Total Internal ReflectionTake refractive index to its critical-angle limit

Key takeaway

Dispersion means one material can assign different refractive indices to different wavelengths.
In this visible model, violet has a larger refractive index than red and therefore bends more in the same prism.
The outgoing fan gets wider when the material response is more wavelength-dependent or when the prism angle is larger.
A no-dispersion prism can still refract the beam; it just stops separating the colors.

Common misconception

A prism does not add colors to white light. It separates wavelengths that were already present because their refractive indices, speeds, and bend angles differ.

The prism is not making new visible colors. It is separating wavelengths that were already present because different wavelengths can use different refractive indices in the same material.

Stay with this concept

Review, test, or free-play here when you want one more same-concept pass.

More practice optionsReview on the bench · Worked examples

Practice optionReview on the benchReplay the guided setup with the key controls and graphs in sight.
Practice optionWorked examplesCompare against solved walkthroughs after you try the setup yourself.
Practice optionFree play on the benchExperiment freely with the live controls before moving to another concept.

Reference and support

Use these calmer sections when you want a fuller explanation, examples, or accessibility support after the guided flow.

Return here when you want the slower reference pass.

Open reference and support

Equation snapshotIndex, speed, and prism spread · Thin-prism deviationShow 3 equations

Start with n(lambda), then use the thin-prism approximation to turn index differences into bend-angle differences.

Index, speed, and prism spread
$n (λ) \approx n_{ref} + D [(\frac{λ _{ref}}{λ})^{2} - 1]$
Gives one material a wavelength-dependent refractive index while staying anchored at a reference wavelength near green.
Thin-prism deviation
$δ (λ) \approx [n (λ) - 1] A$
For a thin prism, the total bend for a given color grows with both refractive index and prism angle.
Color spread
$Δ δ \approx [n (λ_{v}) - n (λ_{r})] A$
Red-violet separation grows when the material is more dispersive or when the prism angle is larger.

Worked examples

Live dispersion checks

Open examples when you want to see the same idea walked through step by step.

Frozen walkthrough

Step through the frozen example

Frozen walkthrough

Read directly from the current prism. The same wavelength-dependent index model drives the stage, the color fan, and the graphs, so each step explains the live picture rather than a separate worksheet.

Supporter unlocks saved study tools, exact-state sharing, and the richer review surfaces that support this guided flow.

View plans

Example 1 of 2

Frozen valuesUsing frozen parameters

For the current wavelength and material, what refractive index does the selected color use?

λ

Selected wavelength

550 nm

n_{ref}

Reference index

1.52

D

Dispersion strength

0.02

1. Use the wavelength-dependent index model

Use

n (λ) \approx n_{ref} + D [(\frac{550}{λ})^{2} - 1]

with wavelengths in nanometers.

2. Evaluate the wavelength factor

For

λ = 550 nm

, the bracket becomes

(\frac{550}{550})^{2} - 1 = 0

3. Calculate the selected refractive index

n (λ) \approx 1.52 + 0.02 (0) = 1.52

Current refractive index

n (λ) \approx 1.52

At 550 nm, the current green ray uses n(lambda) = 1.52, so the thin-prism bend is larger than red but smaller than violet in the same material.

Prism-spread checkpoint

You keep the same prism angle and the same green reference index, but you raise the dispersion strength. Before you touch the controls, which color should separate furthest from the others and why?

Make a prediction before you reveal the next step.

Answer from the wavelength-dependent refractive index, not from brightness.

Check your reasoning against the live bench.

Violet should separate the most because it uses the largest refractive index in this visible range.

Raising the dispersion strength increases the difference between short- and long-wavelength refractive indices. Violet then uses the largest refractive index in the visible range, so it bends the most and pulls furthest from red.

Quick test

Loading saved test state.

Carry color-dependent bending forward

Keep this idea moving

Open the next concept, route, or track only when you want the current model to widen into a larger branch.

Critical-angle limitOptics

Total Internal Reflection

Push a ray from a higher-index medium toward a lower-index boundary, watch the critical angle emerge, and see the same live diagram hand off from ordinary refraction to full internal reflection.

Many surfaces, one bend ruleMirrors and Lenses

Lens Imaging

Trace principal rays through converging and diverging lenses, connect the signed thin-lens equation to the diagram, and watch image distance and magnification respond to the same object setup.

Prism versus line sourcesModern Physics

Atomic Spectra

Link discrete emission and absorption lines to allowed energy-level gaps with one compact ladder-and-spectrum bench that keeps transitions, wavelengths, and mode changes tied together.

Bench tools and share links

Keep stable concept links and exact-state sharing tucked away until you actually need to relaunch or share the bench.

Try this setup

Jump to a named bench state or copy the one you are looking at now. Shared links reopen the same controls, graph, overlays, and compare context.

Current bench

Crown green preset

This bench is currently showing one of the concept's authored presets.

Open default bench

Saved setups

Saved setups are a Supporter study tool. Stable concept links still work for everyone.

Checking saved setup access

Open Model Lab is resolving whether this bench can save locally, sync to an account, or open Supporter-only compare tools.

Copy current setup

Exact-state sharing is part of Supporter. Stable concept and section links still stay available.

Stable links

Progress and next steps

Keep progress signals, starter-track handoffs, and review prompts available without letting them compete with the live lesson flow.

Progress

Loading progress

Loading saved concept progress for this browser or synced account before showing completion status.

Starter track

Step 4 of 5

Wave Optics

Dispersion / Refractive Index and Color appears later in this track, so it is cleaner to start from the beginning first.

Previous step: Double-Slit Interference

Start from track beginning