Colours of Light
Science: KS3, topic 3.3.28
Spectrum of Colours
White light contains all the colours of the rainbow. There are seven colours in the spectrum. Different colours can be added, subtracted, absorbed, and reflected to give different effects.
Spectrum of colours
- You can remember the colours of the rainbow or spectrum using the mnemonic Richard Of York Gave Battle In Vain.
- Red, Orange, Yellow, Green, Blue, Indigo, Violet.
- Each colour has a different frequency.
- You can shine light through a prism to see the spectrum of colours.
Addition of light
- The three primary colours of light are Red, Green and Blue, they can be combined to create secondary colours:
- Red + Green + Blue = White Light
- Green + Red = Yellow
- Red + Blue = Magenta
- Green + Blue = Cyan
Absorption, reflection, and subtraction of light
- When light hits a surface it will either be absorbed or reflected.
- A coloured object only reflects that colour it absorbs all other colours.
- White objects reflect all colours.
- Black objects absorb all colours.
Colour combinations
- A red jumper absorbs all colours apart from red. It reflects red light into our eyes.
- A pair of blue jeans absorbs all colours apart from blue. It reflects blue light into our eyes.
- If you had a green shirt and shone red, green, and blue light onto it only green would be reflected.
- If you had a shirt and shone red, green, and blue light onto it and blue was absorbed. It would reflect red and green. Red + Green = Yellow. So the shirt would appear yellow.
Test yourself on Colours of Light
Which colour combinations are correct?
What colour would a shirt appear if you shone red, green, and blue light onto it and blue was absorbed?
A plain white wall is lit with only green light in a dark room. What colour will the wall look?
A red light is shone onto four objects in a dark room: a white wall, a black T-shirt, a pair of blue jeans, and a green leaf. Which object will look red?