Mysteries of the Microwave
Is a microwave magical? Ask Science explores the science behind microwaves.
In nearly every American home, there sits a microwave oven. We pretty much take it for granted.
But have you ever stopped to consider how it works?
Maybe you know exactly how it works, but if it all seems a bit magical, this week’s episode is for you.
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Why Is a Microwave Called a Microwave?
The reason a microwave is called a microwave is because it uses energy in the form of microwaves to heat food.
Microwaves form part of the EM spectrum, which I talked about in the very first Ask Science episode on radiation. Microwaves are on the low energy side of the spectrum, right between infrared and radio waves.
What makes microwaves special is that they are just the right size to interact with water molecules.
How Does a Microwave Make Microwaves?
It’s magic.
OK, maybe not exactly magic, but pretty close. The technology behind microwaves was developed while trying to perfect radar technology around World War II.
Inside every microwave oven is this thing called a magnetron (which sounds a bit like the name of an evil robot). The magnetron consists of a metal rod called the cathode which is surrounded by a metal doughnut-shaped thing called an anode.
The anode has some holes cut into it around the inside edge, which makes it look like a mouse crawled into the doughnut hole and nibbled a bunch of sections away from the middle. These holes are called resonating cavities. Cavities because they are holes and resonating because of something I’ll tell you in a bit.
While there are a bunch of other parts involved in a magnetron, the last part I’m going to mention are the magnets found above and below the anode doughnut thingy. (Doughnut thingy is not an official term).
To make microwaves, energy is pumped into the cathode rod. As it heats up, electrons start flying off. These electrons are caught in the magnetic field created by the magnets and start spinning around and around the inside of the cathode doughnut hole.
As the electrons pass by the resonating cavities, they resonate with the cavities. This resonance causes the cavities to give off their own energy in the form of microwaves. These waves are then directed into the body of the oven, where they cook your food.
How Do Microwaves Heat Food?
Microwaves are small enough to penetrate a few inches through food. As they do so, they bump into water molecules contained within the food. Since water molecules are polar, one of their ends has a positive charge and the other has a negative charge. This polarity causes the water molecules to try and rotate as they seek to align themselves with the microwave radiation.
As they rotate, they bump into other molecules, causing friction, which generates heat, thereby heating your food.
What Else Should I Know About Microwaves?
Now that you know more about how microwaves work, here are some other interesting facts:
If you don’t have any food in your microwave and you leave it running, the microwaves will bounce back and forth, possibly generating a standing wave, which is an electromagnetic wave that doesn’t appear to move. As the energy of that wave builds, it can burn out the magnetron, ruining the microwave oven.
Another danger is putting metal into a microwave. Depending on the composition and shape of the metal object, microwaves can induce an electric current in the metals, which can lead to electrical arcing, and possibly a fire.
Finally, although most plastics don’t contain water and are therefore unaffected by the microwave radiation itself, as the food heats up, the high temperature of the food can cause the plastic to melt, so always make sure whatever container you’re using is considered “microwave safe.”
Is Microwaved Food Radioactive?
Despite what you might have heard, microwaved food is not radioactive. Remember that microwaves are part of the non-ionizing side of the EM Spectrum; this means that they can’t cause damage to cells like x-rays or gamma rays do.
Putting your food in the microwave is no more dangerous than setting it next to your radio antenna or TV remote control.
That being said, there is considerable evidence that microwaving foods containing oil can cause a chemical change in that oil. The same thing happens when you use any method to heat cooking oil, but microwaves seem to have a stronger effect than a conventional oven. Some studies have shown that unsaturated fats can actually be transformed into trans fats by this process.
Conclusion
So now you know more about microwaves, how they work, and how to avoid setting your house on fire when you use them.
If you have a question that you’d like to see answered in a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email. If you liked today’s episode, you can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein.
No radiation image courtesy of Shutterstock.
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About the Author
Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.
