Remember E=mc2, 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.
- 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
- 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
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?
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.
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
The distance between two melted
spots is half a wavelength
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 of light = wavelength x frequency
The distance between each melted spot should be around 6
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.