Colour and Dispersion
White light splits into colours because each bends differently.
About this topic
White light is a mix of all colours. A prism disperses it because each colour has a different refractive index and bends by a different amount: violet bends most, red least. Rainbows form when sunlight refracts, reflects internally and refracts again in raindrops.
An object's colour depends on which wavelengths it reflects: a red apple reflects red and absorbs the others, and under pure green light it would look black. Filters transmit only certain colours. Newton showed that a second prism can recombine the spectrum into white, proving colours were in the light and not added by the glass.
Worked example: in a rainbow, red appears on the outside of the arc at an angle of about 42 degrees from the point opposite the Sun, and violet on the inside at about 40 degrees. To see one you need the Sun behind you and rain in front. Sometimes a fainter second rainbow forms outside with reversed colour order.
Dispersion also causes colour fringes in cheap lenses, called chromatic aberration, which good cameras fix with combined lens elements. The blue sky comes from scattering, not dispersion. A misconception is that a prism makes colours; it only separates what was already present. Another is that rainbows are fixed objects; each person sees their own.
Key ideas
- Prisms disperse light
- Rainbows are refraction plus reflection
- Red bends least
Quick check
Use cases: where Colour and Dispersion helps
- Homework: review the key idea behind Colour and Dispersion before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Colour and Dispersion without notes.
- Visual learning: play with the interactive lab to see how Colour and Dispersion changes when you adjust its inputs.
- Teaching a friend: explain Colour and Dispersion in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Colour and Dispersion?
White light splits into colours because each bends differently.
What will I learn in Colour and Dispersion?
Prisms disperse light. Rainbows are refraction plus reflection. Red bends least.
Is Colour and Dispersion part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Colour and Dispersion lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Colour and Dispersion?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.