Question
Why can you see the rainbow in the bubbles in your hot chocolate? Is it because of the physical change in making hot chocolate?
Hannah
Answer
Hannah,
That's a good observation, and a good question. You've probably seen similar "rainbows" in soap bubbles. Perhaps even on oily patches in the road. If you look carefully, you'll probably notice that the colors you see aren't as orderly as in a rainbow.
Now, a little bit of background about light...
As you know, normal visible light (sometimes called "white" light) is a mixture of many different colors. Each of these colors has a different wavelength and frequency. What are wavelength and frequency? If you move the end of a long rope up and down, you can get a wave to move down the rope. The frequency is how many times you move up and down in a given period of time, and the wavelength is the distance from one peak of the wave to the next. The product of wavelength and frequency is the speed of the wave.
For light waves moving through air, the speed is always roughly 300,000 kilometers per second (186,000 miles per second). For light that you can see, the wavelength is between about 400 nanometers (violet) and 700 nanometers (red). A nanometer is one billionth of a meter; a meter is a bit more than a yard. So the wavelength of visible light is pretty small. The frequency is between roughly 750 terahertz (violet) and 425 terahertz (red). A terahertz is one trillion cycles per second. By comparison FM radio has a much lower frequency (between 88 megahertz and 108 megahertz
