Remember E=mc^{2}, Einstein's famous equation? The 'c'
stands for the speed of light. You don't need fancy equipment to
measure it. All you need is a microwave, ruler, bar of chocolate
and a calculator.

**How to:**

- Take the turntable out of the microwave. You need the chocolate to stay still whilst you heat it.
- Put a plate upside down over the thing that rotates the turntable (does that have a name? For now I'm going with 'rotator').
- Put your chocolate in the middle of the plate.
- Heat the chocolate until it starts to melt in two or three places. This should take about 20 seconds.
- Take the chocolate out of the microwave - carefully! It will be hot. Measure the distance between the melted spots.
- If your microwave is a standard model, it will have a frequency of 2.45 gigahertz. This means that the microwaves move up and down 2.45 billion times per second. Check in your microwave manual if you're not sure of the frequency.
- Multiply the distance between the spots on the chocolate bar by two. Multiply that by 2,450,000,000 (2.45 gigahertz expressed as hertz).

**Distance between two melted spots of chocolate x 2 x
2450000000 = z**

What answer do you get for z? The speed of light is
**299,792,458 metres per second**.

Remember, if you measured the distance between the melted spots
in centimetres, **z** will be in centimetres per
second. To get an answer in metres per second, divide
**z** by 100.

Was your answer close to the speed of light?

**What's happening?**

Microwaves are a type of electromagnetic radiation, just like light waves. Microwaves also travel at the speed of light. If you measure how fast they are travelling, you should get a result close to the speed of light.

**Wavelength**

When you measure the distance between two melted spots you can work out the wavelength of the microwaves.

Measuring the distance between melted spots gave you half a wavelength. You need to multiply the distance by two to get a whole wavelength.

*The distance between two melted
spots is half a wavelength*

**Frequency**

Now you know the wavelength you need to know the wave frequency. Wave frequency is how many times a wave bounces up and down in one second. This is 2.45 gigahertz in most microwaves. This means that a wave will move up and down 2.45 billion times per second.

**Speed**

**Speed of light = wavelength x frequency**

The distance between each melted spot should be around 6 centimetres.

**6 x 2 x 2450000000 = 29400000000 cm/s**

This is equivalent to 294,000,000 metres per second. That's pretty close to the speed of light!

Now you've satisfied your curiosity, you can eat the chocolate. A well deserved reward for you hard work.

This experiment featured on the Null Hypothesis and Wired.