Did you know we can calculate the speed of light with a bar of chocolates and a microwave oven? It sounds crazy, but it’s easy, and you and your little ones get to eat the chocolate at the end.

It’s all to do with waves. Electromagnetic radiation, the stuff that your microwave oven produces, is a wave that travels at the same speed as light. So, if you can determine the speed of the radiation, you will get the speed of light as well – and, let’s not forget, nothing in our universe travels faster than light!

To calculate the speed of a wave, you simply need to measure its frequency and its wavelength.


Getting the frequency is straightforward. Look at the technical details at the back of your microwave oven, and you will find the frequency of the wave it produces, which is generally at 2,450Mhz or 2,450,000,000 Hertz.

Then, how about the wavelength? Well, luckily for us, this is when chocolates come into the equation. Here’s how it works.

Microwave ovens produce waves of electromagnetic radiation whose peaks and troughs are fairly stable and stay in the same place inside the microwave oven. When a wave hits a piece of food, it warms it. Because the microwaves produced by the oven stay at the same location, only parts of the food are warmed up. This is why food in microwave ovens is placed on a turning plate, so that the heating is distributed across the food and warms up fairly evenly.

But, in this case, you want to see the location of the waves to measure the wavelength, so you need to remove the turning plate. Once this is done, place a large bar of chocolate on a plate inside the microwave oven. Warm the bar of chocolate for 30 seconds to a minute, and you will be able to see the areas where the melting has occurred. This is where the microwaves produced by the oven have hit the chocolate.



Then, all you have to do is take a ruler and measure the distance between the areas where the chocolate has melted.

Since this will give you half of the wavelength, simply times it by two to get the actual length of the wave produced by the microwave oven. In our example, we measured 6 centimeters so 6 x 2 = 12 centimeters.

Now that we have our two numbers – frequency and wavelength – take a calculator and apply this simple equation:

Wave speed = frequency x wavelength.

In our case, the frequency is 12 cm and the wavelength is 2,450,000,000 hertz (cycle per second), so we get :

Wave speed = 12 x 2,450,000,000 = 29,400,000,000 cm per second.

That is the speed of the waves moving in your microwave oven, and that of light as well, although, with finer instruments, you would get a more precise figure of 29,979,245,800 cm per second, or 299,792,458 meters per second!


Try this simple experiment with your children at home, and don’t forget you can all eat the bar of chocolate afterwards. You’ll deserve it.


Written by,

Tinkerer’s Science Team