How a Microwave Oven Works
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How a Microwave Oven Works

Microwave ovens are part of many of our day to day lives. Whether you use them to make popcorn or heat up yesterday's leftovers, they bring a level of convenience for when you just don't feel like using the stove. If you have ever wondered how microwaves cook your food, or why you should never put metal in the microwave, this article will give you a glimpse into what lies beneath the surface.

In order for a microwave to properly operate, it requires the use of an internal high voltage system. This system works by taking the line voltage supplied by the outlet and, through a series of capacitors, up-converts the power output which is then converted to the RF (Radio Frequency) energy that is used to cook your food. The magnetron is the heart of the high voltage system necessary to power a microwave. The magnetron is what is known as a diode-type electron tube. It is used to produce the necessary microwave energy (2450 MHz) for the microwave to work.  

The basic structure of a magnetron includes an anode, a filament/cathode, an antenna and magnets. The anode is a hollow iron cylinder which contains an even number of anode vanes which extend inward towards the center of the tube. The area between these vanes are known as resonance cavities. These cavities serve as tuned circuits that determine the overall output frequency of the electron tube. The segments of the anode are connected in a way that allows each segment to be of the opposite polarity of the segment on either side of it.

The filament, which is also often referred to simply as the heater, is located at the center of the magnetron and serves as the cathode for the electron tube. Next on the list is the antenna. The antenna is connected to the anode and reaches into one of the tuned circuit cavities. It is also coupled with something known as a waveguide, which is a hollow metal enclosure into which the antenna transmits the radio frequency energy. Lastly, the magnetic field, which is provided by high-powered permanent magnets attached around the magnetron in order to align the magnetic field to the same axis as the cathode, directs the flow of electrons generated by the process.

This may all seem confusing at first, but in order to truly understand how the magnetron cooks the food, it is important to know how the individual parts work as one. When all of the pieces work together, it allows the magnetron to generate a large amount of electrons. The magnetic field inside the magnetron begins pumping these electrons back and forth within the tube until they reach the natural resonant frequency of the tube. This action is what leads to the radiation of the electromagnetic waves from the magnetron.

The radiation that occurs from a microwave is not like the radiation we hear about from nuclear power plants. Also, just in case you are wondering, the answer is no, the food you cook in the microwave in no way becomes radioactive no matter how long or how many times you “nuke" it, and it is completely safe to for you to long as you let it cool off a bit first. The radiation in a microwave is a radio frequency created by an electromagnetic field that is expelled into the cooking chamber of the microwave. The electrons that are emitted bounce off the metal chamber of the microwave and excite the water molecules in your food. As the water molecules get excited, they begin to move more rapidly. This rapid motion of molecules causes an increasing amount of friction in your food. That friction creates the heat. The heat from the water molecules is what actually cooks your food.

The metal cooking chamber of the microwave is called a Faraday cage. The Faraday cage is designed to keep the electromagnetic radiation from escaping the microwave while it is operating. If you look closely at the microwave door, you may notice that there is a wire mesh in the glass. This wire mesh is the final wall of the Faraday cage. With that mesh, you are able to see into your microwave as it is operating without worrying about heating up or melting the door. The reason that you can still see through it is because visible light has a much smaller wavelength than the electromagnetic radiation, so while the light can pass through the mesh, the holes are too small to let the electromagnetic radiation through. It works in the same way that a pasta strainer does, were the hot water is the light that goes through the strainer and the pasta is the electromagnetic radiation that is contained.

You have likely heard the warning to never put metal in the microwave. There is a very good reason for this. As mentioned previously, the electrons emitted from the magnetron bounce around the cooking chamber and stimulate the water molecules in your food. When metal is placed in the chamber, the electrons can only bounce off the metal, which is already packed with electrons of its own and the repeated reflections of those electrons ends up generating an electrical charge. Once the charge reaches a certain point, the electrons end up being released in the form of arcs of electricity. These arcs can reach temperatures of up to 35,000 degrees Fahrenheit, which is roughly four times hotter than the surface of the sun. These arcs can burn holes right through the Faraday cage and completely destroy the magnetron. Needless to say, it is probably not something you want to have happen in your nice expensive  microwave oven.

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