CoolTech HowTo

Use a Bar of Chocolate to Measure the Speed of Light

Use a Bar of Chocolate to Measure the Speed of Light
Written by Izak Van Heerden

Attention, chocolate lovers and science geeks! That chocolate bar you’ve been saving for a midafternoon snack can satisfy both your sweet tooth and your scientific curiosity. You can perform a scientific experiment to measure the speed of light using a chocolate bar and a microwave.

Here’s how it works. All electromagnetic waves travel at the same speed. Microwaves and visible light are both electromagnetic waves, so microwaves travel at the speed of light. If you can figure out how fast microwaves travel, your result should be roughly the same as the speed of light.

The equation is wavelength times frequency equals speed, or νλ = c.

To determine the wavelength of microwaves, you can measure the distance between two hot spots in food. A wavelength is the distance between the two peaks of a wave. The wave’s peak and trough are the hot spots, and in between the peak and trough are the cool spots. The distance between the two hot spots is half a wavelength (because the two closest hot spots will be the peak and trough), so you’ll need to multiply the measurement by 2 to get a full wavelength.

The hot and cold spots are why your food needs to rotate in a microwave oven to cook evenly, and they’re the reason cooking instructions often say to stir food halfway through.

Once you know the wavelength, you’ll need to plug in the frequency, or how many times a wave bounces up and down in a second. In most microwaves, the wave frequency is 2.45 gigahertz. This means that the wave bounces up and down 2.45 billion times a second. The frequency of most microwaves can be found on the back of the unit or inside the door.


For this experiment, you’ll need a large chocolate bar, a microwave, a metric ruler, and a calculator.

You don’t want the chocolate bar to heat evenly for this experiment, so you’ll need to be sure it doesn’t rotate as it is being heated. Remove the microwave’s turntable, turn it over, and then put it over the rotators. Turn the microwave on briefly and check to make sure the upside-down turntable doesn’t rotate. You could also use an upside-down plate or tray over the rotators–whatever provides a flat surface that doesn’t rotate.

When you’re sure your large-size chocolate bar won’t rotate, place it in the center of the microwave. Turn the microwave on until the chocolate begins to melt, usually about 20 seconds.

Be sure to remove the chocolate bar when melted spots first begin to appear. For one thing, you don’t want to burn the chocolate because you’ll want to eat it when your experiment is done. For another, you want some areas of the chocolate to be melted and other areas to be solid.

Using a ruler, measure the distance in centimeters between the centers of two of the melted areas. This should be about six centimeters, but be sure to perform the measurement yourself because it’s much more fun.

Now plug your measurement, times two, into the formula: wavelength (the distance between hot spots times two) times frequency (usually 2.45 gigahertz). Let’s say you measured the distance between the hot spots as 5.75 centimeters. Your equation would look like this: 5.75 x 2 x 245,000,0000 = speed of light. You’ll get 281,750,000, which is pretty close to the actual speed of light, 299,792,458.

You could do this with other meltable foods, such as cheese, butter spread thickly on bread, or marshmallows. This is a tiny measurement multiplied by a huge number, so your result won’t be exact, but it’s a delicious way to conduct an interesting science experiment. You can eat your chocolate bar now.

About the author

Izak Van Heerden

Izak has witnessed a couple of decades worth of changing tech. He hopes to make it a couple more until his conscience can be copied to a cyborg body.

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