Sun, 6 May 2007 Microwaves ovens – Hello, and welcome to the How Things Work podcast. My name is Jamie Aycock, and in each episode we’ll explore the inner workings of things we see and use every day. In this episode we’ll explore how microwave ovens work. Microwave ovens were first developed by the Raytheon Corporation in the mid 1940’s. Their invention came about, like so many great inventions, by accident. A radar researcher named Percy Spencer noticed that a candy bar placed near a radar antenna had melted. He repeated this with popcorn (which popped) and an egg (which exploded). It was clear that the radar set was causing these products to heat up. Just what was causing the radar waves to heat these items? Water, as most people know, has the chemical formula H20 – that is to say that there are two hydrogen atoms and one oxygen atom per molecule of water. These three atoms are arranged sort of like a silhouette of Mickey Mouse’s head – one large circle (the oxygen atom) in the middle with two smaller circles (the hydrogen atoms) stuck on top like Mickey’s ears. A water molecule has a dipole moment – a dipole moment simply means that one part of the molecule (the hydrogen) has a positive electrical charge and one part of the molecule (the oxygen) has a negative electrical charge. Imagine a bar magnet set on a needle so it can spin freely. If you were to approach the positive end of this magnet with the positive end of a second magnet, since like forces repel and opposite forces attract, the magnet would spin around so that magnet on the needle came to rest with its negative end towards the positive end of the second magnet. The very same principle is used in a microwave oven. A part of a microwave called a magnetron produces an electromagnetic wave at about 2.45GHz. An electromagnetic wave at 2.45GHz changes from positive to negative and back 2.45 billion times each second. As the positive part of the electromagnetic wave nears a water molecule in food, the water molecule turns so that its negative end (the oxygen end) is closer to the positive portion of the wave. Likewise, the positive end of the water molecule is attracted to the negative part of the wave. As the wave moves, the molecule will move, trying to maintain this arrangement. The end result is that all of the water molecules are constantly moving around, trying to keep their positively charged end near the negative part of the wave and vice versa. As the electromagnetic wave moves, so do the water molecules. All of these water molecules moving around generate heat due to the friction of them bouncing into and rubbing against each other. This heat cooks our food. That’ll wrap things up for this episode of How Things Work. A transcript of this episode can be downloaded from howthingswork.libsyn.com, and if you have any questions, comments, or topic ideas, please drop me a line at howthingswork@verizon.net. Thanks for listening. The music you heard was How’d You Know That by Scott Brown. It’s available on Random Chance records at www.randomchancerecords.com and is made available through the IODA Promonet. Citations – http://en.wikipedia.org/wiki/Microwave_oven http://www.zyra.org.uk/microw.htm http://www.madehow.com/Volume-1/Microwave-Oven.html http://www.lsbu.ac.uk/water/microwave.html http://www.lsbu.ac.uk/water/microwav2.html http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html http://www.rps.psu.edu/probing/microwave.html http://www.colorado.edu/physics/2000/applets/h2o.html http://www.colorado.edu/physics/2000/applets/h2ob.html Category: Show Notes -- posted at: 5:17 PM Comments[1] |
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How Things Work A look into the inner workings of things we see and use every day
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