GCSE Physics · Edexcel 1PH0 · Topic 5B
Colour
Key points
- White light is a mix of all visible colours: red, orange, yellow, green, blue, indigo, violet (red has the longest wavelength, violet the shortest).
- Opaque objects absorb some wavelengths and reflect others; the reflected light gives the object's colour.
- A white object reflects all colours; a black object absorbs all colours.
- Filters transmit only certain colours and absorb the rest; a red filter only lets red light through.
- A blue object seen in red light looks black, because there is no blue light for it to reflect.
- Transparent and translucent materials transmit light; translucent materials scatter it so images are unclear.
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The colour of an object is not something it "has" but a result of which wavelengths of light it reflects or transmits. This sub-topic explains coloured objects, coloured filters and why things look different under coloured lighting.
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