Measure the speed of light… with chocolate!

Published on March 13th, 2012
Measure the speed of light… with chocolate!

The speed of light is an important number that gets used in loads of equations. It’s the c in Einstein’s famous E=mc², for example!

But you don’t need to be the next Einstein to calculate this very important number. All you need is a slab of chocolate (at least 18cm by 8cm), a microwave, a piece of paper towel, a plate, a ruler and a few toothpicks.

Here’s how to do it:

  1. Check the frequency of your microwave. Most microwaves operate at 2,45 Gigahertz (GHz), but it’s best to check for the sign marked RF on your particular model.
  2. Remove the rotating plate and place a bowl over the rotating mechanism in the middle, so nothing will rotate when you turn the microwave on.
  3. Place a piece of paper towel on a plate.
  4. Remove the packaging from the chocolate and place the slab on the paper towel.
  5. Put the plate in the microwave, with the longest sides of the chocolate slab facing the front and back.
  6. Heat the chocolate until it barely starts to melt, stopping the microwave to check every once in a while. It should take 20 to 90 seconds, depending on the strength of your microwave.
  7. Once the chocolate has begun to melt, take it out of the microwave and feel the surface for a pattern of hot melted spots.
  8. Use toothpicks to mark the centre of each hot spot.
  9. Measure the distance between the toothpicks and double it to get the wavelength of light.
  10. Multiply the wavelength (in metres) by the frequency of your microwave to get the speed of light in metres per second.