White Light & Colour
Explain that white light is a mixture of all visible colours (ROYGBIV), describe dispersion through a prism, explain why objects appear coloured (selective reflection and absorption of wavelengths), and describe colour mixing with filters
What a learner can do afterwards
- Lists the colours of the visible spectrum in order of increasing frequency
- Explains why a prism disperses white light into a spectrum
- Explains why a red object looks red under white light but black under blue light
- Predicts the colour of an object seen through a colour filter
The lesson
Light from the Sun or a lamp looks white, but it is not really one colour. It is a mix of many colours travelling together in a single beam of light.
A prism is a triangle-shaped piece of glass. When white light enters a prism, each colour bends by a different amount. Red bends the least, violet bends the most, so the colours spread apart into a fan of colour. This spreading apart is called dispersion, and it shows you the colours that were hiding inside the white light all along.
Zara has a red jumper. In white light, the jumper reflects red light back to her eyes and absorbs every other colour, so it looks red. When Zara shines pure blue light on the jumper, there is no red light for it to reflect. The jumper absorbs the blue light too, so it looks black.
A colour filter only lets its own colour of light pass through, and absorbs the rest. To predict what colour something will look through a filter, check whether the object reflects that filter's colour. If it does, the colour shows through. If it does not, the object looks dark or black.
White light is a mix of every colour, a prism spreads that mix into a rainbow, and an object only shows the colours it reflects, never the ones it absorbs.
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Where it sits
Learn first
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.