How to Measure the Speed of Light with Chocolate and a Microwave

An astronomer measures the speed of a star using light.

Have you ever wondered how fast light travels? Light is the fastest thing in the universe, but it’s not easy to measure its speed. You might think you need a sophisticated laboratory or a giant telescope to do that, but actually, you can do it at home with some simple items: a microwave oven and a chocolate bar. Yes, you read that right. You can use chocolate to measure the speed of light!

In this blog post, I will show you how to do this fun and easy experiment, and explain the science behind it. You will learn how microwaves work, how they interact with chocolate, and how to use them to calculate the speed of light. You will also discover some interesting facts about light and its properties. Ready to get started? Let’s go!

What You Need

To do this experiment, you will need the following items:

• A microwave oven
• A chocolate bar (preferably dark chocolate)
• A ruler
• A calculator
• A plate

What You Do

Here are the steps to follow:

1. Remove the turntable from the microwave oven. This is important because you don’t want the chocolate to rotate while it’s being heated. You want it to stay still so you can see the pattern of melting.
2. Break the chocolate bar into small pieces and scatter them on a plate. Make sure they cover most of the plate, but leave some gaps between them.
3. Put the plate inside the microwave oven and heat it for about 20 seconds, or until you see some of the chocolate pieces start to melt. Don’t overheat it, or you will end up with a messy plate of melted chocolate😅.
4. Take out the plate and observe the chocolate pieces. You should see that some of them are melted and some are not. You should also notice that the melted spots are not random, but form a regular pattern of lines or dots across the plate.
5. Measure the distance between two consecutive melted spots on the plate. This is half of the wavelength of the microwaves that heated the chocolate. Write down this distance in centimeters.
6. Look at the back or inside of the microwave oven and find its frequency. This is usually written on a label or sticker, and it’s measured in hertz (Hz), which means cycles per second. For example, my microwave oven has a frequency of 2,450 MHz, which means 2,450 million hertz.
7. Use your calculator to multiply the distance you measured in step 5 by two, and then by the frequency you found in step 6. This will give you the speed of light in centimeters per second. To convert it to meters per second, divide it by 100.
8. Compare your result with the accepted value of the speed of light, which is about 300,000 kilometers per second, or 300 million meters per second.

How It Works

You might be wondering how this experiment works, and what does chocolate have to do with light. Well, let me explain.

Microwaves are a type of electromagnetic radiation, just like light, radio waves, X-rays, and gamma rays. They are invisible to our eyes, but they can be detected by special devices or by their effects on matter. Microwaves have different wavelengths and frequencies than visible light, but they travel at the same speed in a vacuum: the speed of light.

A microwave oven works by generating microwaves and sending them into a metal box called a cavity. The microwaves bounce around inside the cavity and hit whatever is inside it: food, water, or in our case, chocolate. When microwaves hit matter, they make its molecules vibrate faster and generate heat. This is how microwaves cook food.

However, not all matter absorbs microwaves equally well. Some materials reflect microwaves better than others. For example, metal reflects microwaves very well, which is why you should never put metal objects inside a microwave oven: they will create sparks and damage your oven.

Chocolate absorbs microwaves better than air or plastic, which is why it melts when exposed to them. But chocolate does not absorb microwaves uniformly: it has different ingredients that have different properties, such as cocoa solids, cocoa butter, sugar, milk solids, etc.

These ingredients create tiny variations in the density and electrical conductivity of chocolate, which affect how well it absorbs microwaves. As a result, some parts of chocolate absorb more microwaves than others and melt faster.

But why do these melted spots form a regular pattern? That’s because microwaves also interfere with each other inside the cavity.

Interference is a phenomenon that occurs when two or more waves meet and combine their effects. Depending on how they meet, waves can either add up or cancel out each other. When waves add up, they create a bigger wave. When waves cancel out, they create a smaller wave or no wave at all.

In our experiment, the microwaves inside the cavity form a standing wave pattern. This means that some points in the cavity have high intensity microwaves, and some points have low intensity or no microwaves. These points are called nodes and antinodes, respectively.

The distance between two consecutive nodes or antinodes is half of the wavelength of the microwaves. The wavelength is the distance between two identical points on a wave, such as two peaks or two troughs.

The chocolate pieces on the plate are exposed to different intensities of microwaves depending on where they are located. The chocolate pieces that are at the antinodes, where the microwaves are strongest, absorb more microwaves and melt faster. The chocolate pieces that are at the nodes, where the microwaves are weakest or nonexistent, absorb less microwaves and remain solid.

By measuring the distance between two melted spots on the plate, we can find half of the wavelength of the microwaves. By multiplying this distance by two, we can find the full wavelength. By multiplying this wavelength by the frequency of the microwaves, we can find their speed.

This is based on a simple formula that relates the speed, wavelength, and frequency of any wave:

c = λf

where c is the speed of the wave, λ is the wavelength of the wave, and f is the frequency of the wave.

Since microwaves are a type of light, their speed is equal to the speed of light. Therefore, by using this formula, we can estimate the speed of light with a microwave oven and a chocolate bar.

What You Learn

By doing this experiment, you can learn some interesting facts about light and its properties. Here are some of them:

• Light is not only what we see with our eyes, but also a form of electromagnetic radiation that includes microwaves, radio waves, infrared rays, ultraviolet rays, X-rays, and gamma rays. All these types of light have different wavelengths and frequencies, but they travel at the same speed in a vacuum: about 300 million meters per second.
• Light can interact with matter in different ways: it can be reflected, absorbed, transmitted, refracted, diffracted, scattered, or polarized. These interactions depend on the properties of light and matter, such as their wavelength, frequency, energy, density, electrical conductivity, etc.
• Light can also interfere with itself and create patterns of high and low intensity. These patterns depend on how light waves meet and combine their effects. Interference can be constructive (when waves add up) or destructive (when waves cancel out).
• Light can be used to measure distances and speeds in various ways. For example, astronomers use light to measure how far away stars and galaxies are from us by using methods such as parallax, redshift, or standard candles. Scientists also use light to measure how fast objects move by using methods such as Doppler effect or time dilation.

What You Think

I hope you enjoyed this blog post and learned something new about light and its properties. I also hope you had fun doing this experiment and measuring the speed of light with a microwave oven and a chocolate bar.

Now I want to hear from you: what did you think of this experiment? Did you get a result close to the accepted value of the speed of light? Did you encounter any difficulties or challenges? Did you try different types of chocolate or other foods? Did you find any other ways to measure the speed of light at home?

Please share your thoughts and experiences in the comments section below. I would love to hear your feedback and suggestions for improvement. Also, feel free to ask any questions you might have about this topic or any other related topics.

Thank you for reading this blog post and for being curious about science. I hope you will continue to explore and discover new things every day. Remember: science is everywhere, and it’s fun!

References

• Hood, N. (2007). Measuring the Speed of Light in the Kitchen. Retrieved from https://www.fife.ac.uk/faculties/avs/Documents/Measuring%20the%20Speed%20of%20Light.pdf
• Stauffer, R.H., Jr. (1997). Finding the Speed of Light with Marshmallows — A Take-Home Lab. The Physics Teacher, 35, 231–232. doi: 10.1119/1.2344684
• Olson, A. (n.d.). Measuring the Speed of ‘Light’ with a Microwave Oven. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p056/physics/measuring-the-speed-of-light-with-a-microwave-oven
• Delbert, C. (2020). How to Measure the Speed of Light With a Bar of Chocolate and Your Microwave. Retrieved from https://www.popularmechanics.com/science/a34199482/chocolate-microwave-speed-of-light-experiment/