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Measure the Speed of Light with Chocolate and a Microwave!

Measure the Speed of Light with Chocolate and a Microwave!

Did you know that you can measure the speed of light with a chocolate bar and a microwave?

It's quantum mechanics, in your very own kitchen.

Here’s a really cool intersection of food and science that deserves attention: did you know that you can measure the speed of light using chocolate, a microwave, and a ruler?

All these humble instruments can come together to help you conduct “kitchen quantum mechanics,” as one researcher.

In order to measure the speed of light in your microwave, you’ll need to stop the plate inside from moving, so remove the wheels. Next, lay your chocolate flat in the microwave and set on high for 15 seconds.

By measure the distance between the melted and soft portions of chocolate on the bar you’ll find the wavelength, which you’ll multiply by the frequency (waves per second) of your microwave. Yes, it is more complicated, but I’ll leave the explanations to the team at the Bristol Science Center.

Watch the video below:

For the latest food and drink updates, visit our Food News page.

Karen Lo is an associate editor at The Daily Meal. Follow her on Twitter @appleplexy.

There’s an Easy (And Tasty) Way to Measure the Speed of Light at Home

The first successful measurement of the speed of light took place in 1676. Danish astronomer Ole Rømer was trying to measure the orbit of Io, Jupiter's third largest moon, by watching how long it took to pass around the planet. Watching Io over many years, Rømer made a surprising discovery, says the American Museum of Natural History:

The time interval between successive eclipses became steadily shorter as the Earth in its orbit moved toward Jupiter and became steadily longer as the Earth moved away from Jupiter. These differences accumulated. From his data, Roemer estimated that when the Earth was nearest to Jupiter. eclipses of Io would occur about eleven minutes earlier than predicted based on the average orbital period over many years. And 6.5 months later, when the Earth was farthest from Jupiter. the eclipses would occur about eleven minutes later than predicted.

Roemer knew that the true orbital period of Io could have nothing to do with the relative positions of the Earth and Jupiter. In a brilliant insight, he realized that the time difference must be due to the finite speed of light.

Before Rømer, scientists were unsure if light had a limited speed or if its speedometer was permanently stuck at “infinite.”

A few hundred years later, techniques for measuring the speed of light have grown astoundingly more precise and, in some cases, more complex. But in the video above, the folks at the At Bristol science center show off a relatively simple way to calculate the speed of light that doesn't involve years of looking through a telescope eyepiece. In fact, their approach uses nothing but simple kitchen equipment—and chocolate.

In the video, hosts Ross Exton and Nerys Shah use little more than a microwave oven and a chocolate bar to show how to calculate the speed of light. The video doesn't make it perfectly clear how measuring the melted bits on a chocolate bar relates to the speed of light. But breaking it down a little more just requires taking a look at some of the units used in their measurements.

Hertz is the physics stand-in for “cycles per second.” The microwave used in the video produced light waves with a frequency of 2,450,000,000 Hertz, or that many cycles per second. Going from peak to peak in a wave—in this case the distance between the first and third melted bit of chocolate—is one cycle. Exton and Shah measured that distance as 0.12 meters, or 0.12 meters per cycle. Multiplying something measured in “meters per cycle” by something in “cycles per second” will give a measurement in “meters per second.” That's the wave's velocity—the speed of light.

The trick that makes the At Bristol team's approach work is that we in the modern era already know a few important things about light: that it has a finite speed, and that that speed is largely constant. We also have the benefit of physicists having already teased out the relationship between wave length, frequency and velocity.

When Ole Rømer looked to Jupiter and first deduced the speed of light he came up with 214,000,000 meters per second. “This measurement, considering its antiquity, method of measurement, and 17th century uncertainty in exactly how far Jupiter was from the Earth, is surprisingly close to the modern value of [299 792 458] meters per second,” says Dave Kornreich for Cornell.

Using a microwave and a chocolate bar Exton and Shah got 294,000,000 meters per second—not bad for a little bit of kitchen science.

Measure the Speed of Light Using Your Microwave

Astronomers studying star formation, like myself, use telescopes that can see though the pretty, optical exteriors of nebulae into the dark interiors where very cold dust radiates in the submillimetre and microwave regimes.

Microwaves, fall on the electromagnetic spectrum, between radio waves and infrared waves. They are usually around the size of a few centimetres and you may well be very familiar with them as they are produced by the microwave oven that might just be sitting in your kitchen.

Microwave ovens use a particular microwave frequency to excite molecules of water. Since water is present in lots of food and drink, this means that microwaves heat up lots of useful stuff – and they do it quickly. The fact that microwaves are now readily available to most of us in the western world and they are only a few centimetres in length, means that you can measure the speed of light in your very own home.

What You Need:

The quickest and tastiest way to perform this little experiment is with marshmallows, but chocolate chips also work. You’ll obviously need a microwave oven as well, and a large, microwaveable dish. You will need a ruler, too.

Get your large, microwaveable dish and place a layer of marshmallows at the bottom of it.Remove the turntable from the bottom of the microwave oven. If you don’t, then this experiment will not work at all. If your microwave doesn’t have a turntable, it means that the turning mechanism is elsewhere and you’ll need to find a regular microwave oven to try this experiment.

Cook the marshmallows on a low heat for a couple of minutes, or until you see parts of the marshmallows starting to bubble. When you do, remove the dish and take a look at the marshmallows.

You ought to see that they have not melted evenly. In fact you should be able to see a regular pattern has formed, drawn out in melted-mallow. It depends on your microwave oven, but you should see a melted/unmelted pattern across the dish in some direction. When I tried it at home, my oven created long melted strips next to long unmelted strips (see above).

This regularity is caused by the same mechanism that heats up the food you place into your microwave oven. The appliance generates microwaves which very quickly form standing waves (see animation above) inside the cavity inside, where you put food. As the food rotates around, it passes through the standing wave nodes and this excites the water molecules, heating the food.

Measure the Microwaves:

Take your ruler and measure the distance between the melted parts of the marshmallows. You should find that there is an even pattern of melting and that the distance between them is something like 5 or 6cm. Why? Because that is the distance between the nodes of the standing waves.

Without the rotating mechanism, the food does not move around and cook evenly, instead it just heats at the nodal points. Using your marshmallows you have created a ‘map’ of the microwaves in your microwave oven!

Find the Frequency:

Finally you need to know the frequency at which your microwave oven operates. It is usually written on the back somewhere in small writing. Most standard microwave ovens operate at 2450 MHz. If you cannot find the value on the back of the oven, you can take it for granted that 2450 MHz is about correct.

Measure the Speed of Light:

Now you have what you need to measure the speed of light. You just need to know a very fundamental equation of physics:

Speed of a Wave (c) = Frequency (f) x Wavelength (L)

The distance between the melted sections of the marshmallow is in fact L/2, because there are two nodes for each wave (see animation). So if you have measured 6cm and your oven operates at 2450 MHz, then your measured speed of light is (0.12 x 2450,000,000) 294,000,000 metres per second.

The agreed value of the speed of light through a vacuum is 299,792,458 metres per second. See how accurately you can measure it? what could you do to make the experiment better, and thus get a closer answer?

Use Your Microwave to Measure the Speed of Light

Can your microwave oven really measure the speed of light? Yes, it can be done. And since many of the suggested experiments also involve chocolate, it will be done. Oh yes, it will be done.

First, a brief summary of the facts:

Microwaves are part of the electromagnetic spectrum. The electromagnetic spectrum includes radio waves, infrared waves, visible light, and ultraviolet, and can best be described as a bunch of things that behave the way visible light does, even though we can't see them, which is a shame, since that would eliminate the need for recreational drugs. Microwaves move at the same speed that light does.

Microwave ovens produce microwaves in a special configuration, called a standing wave. A standing wave. A standing wave is a wave that so perfectly fits its container that it looks like it looks like it's standing still. Most people have created standing waves as children playing with jump ropes. If you lift and push at just the right times, the jump rope will have one place that moves into peaks and valleys, while staying still at the two ends. If you put a little more effort into it, you can make the jump rope have two places that form peaks and valleys, and three points where it seems to be holding still.

This s-like curve is one wave, and the length of it is one wavelength. (Yes, I know that that's obvious. Just bring that up whenever people complain that physics is hard.)

Inside the microwave, the peaks and valleys of a standing wave translate to big time oscillation, and that oscillation cooks the food. The nodes, or places where the jump rope seems to stand still, translate to no oscillation.

That's why the microwave tray rotates. It has to move the food in order to make sure that every part of your frozen dinner is exposed to the places of highest oscillation. If it just stayed still, the peas would be roughly at the temperature of the center of the sun, and be little green time bombs waiting to nuke your tongue, while the tater tots would be frozen, ready to break your teeth when you bite into it. Because frozen foods hate us as much as we hate them. It's inarguable. That's why I put it in the ‘facts' section.

The number of waves that blow by a certain point per second is said to be the frequency of the waves. The frequency, the wavelengths, and the speed of waves have been established as having a set relationship with one another.

(Frequency) x (Wavelength) = Speed

This makes sense both logically and experimentally. For example, if you were sitting on the side of a one mile loop trail, and a runner ran past you once every ten minutes, you could determine their speed like this:

(6 loops per hour) X (1 mile per loop) = A speed of six miles per hour.

If six full waves cycled past you in one hour, the speed would be the same.

And so, we are armed with all the theoretical knowledge we need. Into the fray!

Every site I've been to agrees that you'll need a metric ruler and a microwave with the product label still attached, but the rotating tray brutally ripped out. They disagree, however, on the proper experimental material to nuke. Some sites say you'll need whipped egg whites on a plate. Others favor marshmallows in a dish. I'm going to recommend you go with the ones that recommend either wide chocolate bars or a layer of chocolate chips over a tray. Unless you can find chocolate marshmallows.

Speed of Light in a Microwave (with marshmallows!)

In your senior science studies, you may have learned about Hertz and his experiments with what we now recognise as radio waves. Through a series of experiments, he was able to demonstrate that the mystery radiation he was creating with the sparks from an induction coil behaved not only as a wave, by demonstrating that it showed the wave behaviours of reflection, diffraction, refraction and interference, but also that it was a transverse wave , demonstrated by the fact it could be polarised, just like Maxwell’s predicted electromagnetic radiation .

Many of Hertz’s experiments relied on his being able to use the reflection and interference properties of the mystery waves to create standing waves.

Standing waves are formed when a wave is reflected back and forth between surfaces n/2 wavelengths apart, where n is a positive whole number. The wave interferes with itself, creating static nodes, or areas where the amplitude is always zero, and antinodes , or areas where the amplitude varies between the absolute maximum and minimum values for the wave. For a sinusoidal wave, the spacing between any node to its nearest neighbour node, or antinode to its nearest neighbour antinode, is one half-wavelength.

Microwave ovens rely on the same principle. If you look inside your microwave, you will notice that the entire inside is made of metal, either solid pieces, or pieces perforated with small holes like on the door. (There’s usually also a rectangle that doesn’t look like it’s properly attached to the wall — that’s where you’ll find the antenna that produces the microwaves.) These are both very effective microwave mirrors. This not only shields the outside world from the microwaves generated inside the microwave oven, but also maximises the cooking efficiency by containing the energy in standing waves inside the microwave oven, and then rotating the food you are trying to heat so it passes alternately through areas of high and low intensity. Because of this, you can treat your microwave oven as a scaled down model of Hertz’s lab. The space is scaled down, and so is the wavelength of the radiation.

Maxwell not only predicted the existence and nature of electromagnetic waves, he was even able to predict their speed. The relationship between the wavelength, frequency and speed of a wave is a simple one: v = f•λ. Hertz was able to measure the wavelength and frequency of his mystery waves, thanks to being able to make standing waves, and thus he could easily calculate their speed. This speed was found to agree with Maxwell’s prediction, and also fell within the experimental error range of other scientists’ measurements of the speed of light .

There is a straightforward experiment you can do using your microwave oven to determine the speed of light using exactly the same principles Hertz did.

  • A microwave oven with a removable rotating plate
  • A large, flat, microwave-safe plate or board
    • Mini marshmallows. Please note that the resolution given by full-sized marshmallows is inadequate. Alternatively, you could use:
    • Shaved cooking chocolate. (Note: please use cooking chocolate. Other forms don’t melt adequately, or burn. The author has tried this experiment with Flake bars, which not only burn but produce large amounts of surprising green smoke.)
    • Cheese, of any sort. It will melt, sweat, or in the case of wrapped cheese slices, dessicate or burn quite nicely.
    • Thermal paper, e.g. fax paper roll. Not recommended, because it is not delicious.

    Step 1: Remove the rotating plate from the microwave. If the T- or X-shaped piece that drives the rotation is removable, remove this too.

    Step 2: Spread your marshmallows (or alternative) evenly across your plate or board. Place the plate or board into the microwave, taking care to ensure it is level, and that it will not rotate.

    Step 3: Run the microwave at full power for 30 seconds. If this has been inadequate to cause regions of heating and/or melting, without moving the plate, you can run for additional 10 second bursts until the desired effect is achieved. If you are using marshmallows, they will inflate during heating, but do deflate again fairly quickly once they are allowed to cool slightly. This is okay: once deflated, you will usually find they have shrunk and melted slightly, so it is still possible to tell the “hot spots” from the rest.

    Note that the longer heating takes/the more times you need to reheat, the more sideways heat transfer there will be, and therefore the wider the “hot spots”. In the above photograph, some extra re-heating was performed to maximise the puffiness of the marshmallows for the photo, and you can see how wide the “hot spots” have become.

    Step 4: Measure the distance between two nearest-neighbour “hot spots”. This is your λ/2 value. But how do you find the frequency? It might seem a little like cheating, but because you can’t measure it directly without pulling your microwave apart and putting yourself in danger, you need to take advantage of the sticker on the back of the microwave oven that tells you about its operating parameters. Included on this sticker is the microwave frequency your oven uses. As you can see, the microwave oven used for this demonstration uses a frequency of 2450 MHz.

    Step 5: Eat the melty marshmallowy mess.

    In this demonstration, was found to be 7 ± 1 cm. f was given as 2450 MHz.

    Therefore we can calculate:

    This is about right, but a little off. There was some uncertainty in my measurement of the half-wavelength, though, which I can now include in my answer. I recorded an uncertainty of 1 cm. I can convert this to a percentage of 7 cm, and then back to an uncertainty value in my final calculated speed.

    Uncertainty in c = (0.14×3.4)×10^8 = 0.5 × 10^8 m / s,

    meaning my final answer should be expressed as c= (3.4 ± 0.5) × 10^8 m / s

    The true value of the speed of light in air, 3.0 × 10^8 m / s, falls within this range.

    Leftover Valentine's Chocolate? Use It to Measure the Speed of Light

    To revist this article, visit My Profile, then View saved stories.

    To revist this article, visit My Profile, then View saved stories.

    If you're a long-time reader, you may remember the great leftover Easter Peeps microwave experiment. Well, today we're going to be nuking leftover Valentine's Day chocolate to demonstrate one of the constants of physics, the speed of light. Chocolate makes a very appropriate medium, because the heating property of microwaves was first discovered by a scientist whose candy bar melted in his pocket when he got too close to a microwave device being tested for use in radar.

    WARNING: This experiment may take several tries to get right. We are not responsible for any weight gained. To avoid familial strife, be sure to only do this experiment with your own chocolates or with candy which you have been authorized to access. You can probably find some leftover boxes on sale this week.

    The demonstration works because microwave ovens produce standing waves -- waves that move "up" and "down" in place, instead of rolling forward like waves in the ocean. Microwave radiation falls into the radio section of the electromagnetic spectrum. Most ovens produce waves with a frequency of 2,450 megahertz (millions of cycles per second). The oven is designed to be just the right size to cause the microwaves to reflect off the walls so that the peaks and valleys line up perfectly, creating "hot spots" (actually, lines of heat).

    What you do with the candy is to find the hot spots and measure the distance between them. From that information, you can determine the wavelength. And when you multiply the wavelength by the frequency, you get the speed! Here's what you do:

    1. Make sure the candy is in a microwave-proof box. Better yet, take the chocolate out and put in a microwave safe dish.
    2. Remove the turntable in your oven. (You want the candy to stay still while you heat it.) Put an upside-down plate over the turning-thingy, and place your dish of candy on top.
    3. Heat on high about 20 seconds.
    4. Take the chocolate out and look for hot spots. Depending on the candy you use, you may have to feel the candy to see where it has softened. With the cherry cordials we used, we saw several shiny spots and one place where the chocolate shell melted through, releasing the sweet syrup inside.
    5. Measure the distance between two adjacent spots. This should be the distance between the peak and the valley (crest and trough) of the wave. Since the wavelength is the distance between two crests, multiply by 2. Finally, multiply that result by the frequency expressed in hertz or 2,450,000,000 (2.45 X 10 9 for my son who is just learning scientific notation).

    In our trial, we measured a distance of roughly 6 centimeters. 6 x 2 x 2,450,000,000 = 29,400,000,000 centimeters per second, or 294,000,000 meters per second. This is awfully close to 299,792,458 meters per second, which is the speed of light. Not bad for some leftover chocolate and a kitchen appliance!

    I discovered this experiment at Null Hypothesis, although it can be found all over the Internet, including many versions with fancy charts and animations. By the way, melted chocolate bars are perfect as ice cream topping. Just saying.

    Using a microwave oven and chocolate to measure the speed of light

    I've been teaching science/physics for quite a while, and written lots of stuff along the way. Much of what I've written is for Nelson Thornes, OUP and SamLearning, but here are some things that are properly mine and I can publish here. Hope you find them useful. At you'll find some more items, and minisites about gcse radioactivity, energy resources and the electromagnetic spectrum which can occupy a class for a whole lesson and more.

    Share this

    Remove the turntable from the microwave oven, place a large bar of chocolate in there (maybe raise it a bit on a plastic plate).
    Run the microwave oven, with luck and skill you can get melted chocolate spots at the antinodes.
    Measure the distance between the spots, double it and you have the wavelength. Look up the frequency on the back of the microwave oven, use the wave equation and calculate c. Then eat the chocolate.


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    Remove the turntable from the microwave oven — including the wheels if your microwave has them. Place microwaveable tray upside down over the center rotator in the oven and turn on for 5 s. (If the tray rotates, you might need to use a larger platform, like a paper plate.) You do not want your chocolate bar to move in the microwave. Put the chocolate bar upside down on the back of the tray (see Image 2).

    No safety issues are associated with this activity. When the activity is finished, just consume any and all of the chocolate you want.

    Materials Used in this Experiment:

    • Long chocolate bar – $2.00, $3.50 in NYC
    • Microwave Oven: $100
    • Plate: Clean, preferably. (Microwave safe if you like your microwave)
    • Calculator: Not a must (but see the section titled Time for experiment)
    • Ruler:

      Practical Applications:

      There are many applications to knowing the speed of light, and mentioning all of them would be a crazy, crazy task even for me. However, for the sake of consistency, here are a few interesting scientific applications that use the speed of light:

      • GPS Systems can pinpoint signal location on earth with calculations based on the speed of light.The GPS device (in your hand, for instance) receives a locator beam from multiple satellites at various locations in orbit. At any given time, GPS satellites are located over different parts of the Earth, and they all send out a signal synchronized to each other according to an atomic clock.In other words, they all broadcast at exactly the same time.But because the satellites are at different distances from you, your GPS unit will receive these synchronous signals at different times.Why?Because the signals, despite being broadcast at the same moment and traveling at the same speed (of light!) arrive at your location in a staggered manner – sooner from closer satellites, later for farther ones.Calculating the relative delays of the signals lets your GPS unit figure out where you are to an exceptional degree of accuracy.
      • Communication in Space: The speed of light affects communication in general (since light itself, as we said, is an electromagnetic wave, just like radio waves but at a different frequency) but the most noticeable effect is on communication in space. When Houston ground control (as in, “Houston.. we have a problem!”) communicated with Apollo 8, the first Apollo mission to orbit the moon, they had to wait about 3 seconds until their messages reached the astronauts.
      • Distances in Space: Because distances in space are so vast and the speed of light is constant in a vacuum and thus the same number always, distances to far solar systems, planets and other stellar objects are often referred to in “light years.” In colonel general, the units of “parsec” (“parallax second”) and kilometers are used, but to convey the sheer size of those distances, they are expressed in terms of the speed of light.
        This method of measurement is defined as the distance a light beam travels in a certain amount of time. For example, expressing the distance to Alpha Centauri system as 4.3 light years (meaning light from there takes 4.3 years to reach the Earth) is much more comfortable than trying to say, write, type or remember it as a distance of 4.06802721 * 10^13 km.

      Isn’t light brilliant?- I know, I didn’t laugh either.

      Remember: True science is about experimentation and observation. If you use your brain to do some thinking, the world is at your feet!(Of course the world is at your feet anyway, but if you don’t think you won’t know what to do with it.)

      (lots of thanks to Daniel, who helped me out with English, jokes, and a decent way of combining the two.)

      .11 if you buy by the thousands.
    • Personal, intimate knowledge of the speed of light: Priceless

    Measuring the speed of light melting cheese in a microwave oven

    In this video you see my son Tom and I conducting a simple, yet important experiment, that allows you to approximate the speed of light only using a microwave oven and cheese. How? Well the speed of light is equal to the frequency times the wavelength. And a microwave oven comes with an indication in the back that shows the frequency. Ours is 2450 MHz. So then all you need to do is to melt cheese in a plate and with a simple ruler measure the distances between the first two areas in the cheese that start melting. In order to do this it is important that you prevent the platter of the microwave from turning. For other details just watch the video.

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    It´s a good way to show the nature of the waves (no matter its frecuency) but inside the microwave you don´t have a “pure” wave because the waves are reflecting so in fact you don´t have a pure wavelength equivalent to those 2450 MHz. Anyway, well done very instructive. In Spain are not used to show “practical” demonstrations of the theory. Congrats.

    Watch the video: How to measure the speed of light - with CHOCOLATE! Do Try This At Home. We The Curious