In 1666 young Isaac Newton made a hole in his window shutter and let a beam of sunlight through a glass prism. On the wall appeared a band of colors.
Key idea
White light is a mix of all the colors: red, orange, yellow, green, blue, indigo and violet (the letters ROY G BIV help you remember). A prism, or raindrops, bend each color a different amount and spread them apart.
A rainbow appears when the Sun is behind you and rain is in front of you. Each raindrop acts like a tiny prism.
Why it works
A red apple looks red because it reflects red light and soaks up the other colors. A white shirt reflects all colors; a black one soaks up nearly all of them, which is why black clothes get hot in the sun.
Worked example: Under red light
In a room lit only by red light, what color does a white sheet of paper look?
- White paper reflects whatever light hits it.
- Only red light hits it.
Answer: Red.
Common mistake
Thinking the prism adds the colors. Newton showed the colors were in the sunlight already; a second prism can mix them back into white.
Try it at home
- On a sunny morning, stand with your back to the Sun and spray a fine mist from a garden hose.
- Look for a rainbow in the spray. Which color is on the outside of the bow?
- Or set a glass of water on a sunny windowsill and look for colors on the floor.
Going further. Newton: Optics (the young readers' path tells this story), and Color in Physical Science.