Microwave Oven Experiments Over the years I've indulged my fascination with microwave ovens by doing unwise experimentation. Disclaimer: This information is presented for your information only. Anyone who tries to duplicate these demonstrations does so entirely at their own risk. There is a chance that you will damage your microwave oven. There is a chance that you will cause a fire. They're Heeeeere! Years ago I was living with roomates, and while working in the kitchen I noticed that the florescent light over the sink was about 8 inches long. A light went on in my brain ;) because I'd always wondered what would happen if a flourescent tube was placed in a microwave oven. In theory the RF energy should have enough voltage to ignite the mercury vapor into a plasma, and the lamp should light. But standard ovens put out at least 500 watts, so the tiny flourescent tube should light quite bright, to say the least. I'd never encountered a flourescent tube which was short enough to fit. So, I pulled out the tube, stuck it in the oven, said "THEY'RE HEEEEEERE!" , and punched the ON switch. Sure enough, the kitchen was lit up by a blue-white blaze of light coming from the front of the microwave oven. I only let it run for about 1 second, but this was enough to heat the flourescent tube so it was too hot to touch. Snifter of Neon While working on a microwave article for an encyclopedia, it crossed my mind that it might be possible to map the pattern of RF energy in the oven by filling it with low pressure gas. The gas would glow in proportion to the RF electric field in various parts of the oven's volume. This would be an involved bit of construction to pull off, so I did the next best thing. I grabbed a big bag of NE-2 neon pilot lights and stuck them into a wineglass, hoping that this small volume would show some patterns when the glass was rotated by the oven's turntable. I filled the glass with water, to give the oven something to heat so it wouldn't be damaged by the small load presented by the bulbs. I ran the oven, and the bulbs glowed REALLY BRIGHT. As the turntable turned, various bulbs extinguished and others lit up. However, I could see no coherent patterns. When I emptied the glass, I discovered that several of the bulbs were stuck together. The short metal leads of some bulbs had melted into the glass of adjacent ones. Also, several of the bulbs had small holes melted through their glass, and were full of water. Apparently the plasma temperature was so high that it heated the glass to melting. Or, possibly some corona discharges developed between the inside and outside of the bulbs and burned through the glass. Foil-eating Plasma I'd seen flames produced by microwave ovens before. In the strong RF field, even the tiniest flame will absorb a large percent of the many-hundred-watts oven output. Thousand watt candle? So, I decided to try initiating an electrical flame-discharge intentionally. I tore aluminum foil into 2" squares, crumpled it lightly so it didn't lay flat, then placed it on the oven turntable with the two pieces in light contact. Sure enough, when the oven was turned on there was a loud buzz and a bright light, and a flame erupted from the contact point between the two pieces of foil. When I looked in on them, I found that the brief flame had eaten a bite about the size of a dime out of both pieces. Mapping the Energy Nodes Microwave ovens cook unevenly because a pattern of standing waves forms inside the oven chamber, and the pattern creates an array of hotspots throughout the oven's volume. An operating frequency of around 2000 MHZ will produce a wavelength of around 10cm, and the hotspots should be at halfwave points, or every 5cm, but in a complex 3D pattern. I'd always wondered how this could be visualized. Perhaps fill the entire oven with raw eggwhites, then let the oven cook them into an interesting white, rubbery 3D sculpture? Or fill the oven with solid wax, and let the RF hotspots melt out a 3D structure of holes? Finally someone figured it out: Alistair Steyn-Ross and Alister Riddell, STANDING WAVES IN A MICROWAVE OVEN, The Physics Teacher October 1990, Vol. 28 No. 7 pp474-476 Steyn-Ross and Riddell were stimulated to investigate the pattern of melted cheese on an oven-cooked pizza. They hit on the use of Cobalt Chloride soaked paper. When wet, CoCl solution is pink, but turns sky blue when dry. (It's sometimes sold as "weather indicator" paper) They discovered that this worked beautifully, and a large square of the paper would give varying patterns of pink and blue when supported at different heights on a tile of cork within the oven. Some Microwave Oven Myths Do Microwave Ovens cook from the inside out? Nope. Food is partially transparent to the radio waves, so the energy is able to shine through it, but at the same time the waves are absorbed by the food. Most of the heat is produced in an outer layer about an inch thick. So, large pieces of meat will be quickly cooked to a depth of about an inch, while the inside portions are cooked by heat conduction, just like in a conventional oven. If I put a fork in the Microwave, will it destroy the oven? Nope, this is a myth, but it has some roots in reality. In order to safely use metals inside a microwave oven, the cook would have to learn numerous complex and mysterious rules in order to avoid fires and undercooked food. For example, thin metal will heat up fast in the oven, and may cause fires. The famous problem of the staple in the paper popcorn bag comes to mind. If a metal object is touched to another one or to the metal wall of the oven, an electric arc might ignite there and if not stopped it can set fire to the oven. Sharp conductive points can initiate a corona discharge, a "Saint Elmo's Fire" which behaves the same as a flame and can set fire to the oven if allowed to continue. So it's much easier to totally ban the use of metals in microwave ovens. Aren't these ovens tuned so they only heat water? No. The usual operating frequency of a microwave oven is nowhere near the resonant frequency of water, and the RF energy will heat other substances. For example, drops of grease on a plastic microwave dish can be heated far hotter than 100C, and cause the mysterious scarring which frequently occurs on plastic utensils. Any molecule which is "polar" and has positive and negative ends will be rotated to align with the electric field of the radio waves in the oven. The vibrating electric field vibrates the water molecules (and any other polar molecules) within the food.