MAIN PAGE | AWARDS | WEIRD SCI. | TESLA COILS | HELP! Unwise Microwave Oven Experiments ------------------------------------------------------------------------ Are you a kid? Does your microwave oven belong to your parents? If so, then don't even THINK about trying any of these experiments. I'm serious. If I wreck my microwave oven, I can buy another. Also, I'm a professional electrical engineer. I know enough physics and RF effects to take correct safety precautions when experimenting. But you don't know the precautions, so you should be smart: read and enjoy my writing, but don't duplicate my tests unless you grow up to become an electronics tech, engineer, etc., and buy your OWN microwave oven. ------------------------------------------------------------------------ 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. There is a chance that a heated object will explode. Messing with a microwave oven is stupid if you don't know what you're doing. ------------------------------------------------------------------------ * Microwave demos * Untried experiments * Links to other sites * Microwave oven myths 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 brightly, to say the least. I'd before never encountered a flourescent tube which was short enough to fit in an oven. 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. (There are better ways to do this, some below.) 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. Hot glass is conductive, so the arc would continue once started. Foil-eating Plasma I'd seen electrical 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 and grow large. 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 foil pieces adjacent to each other and in gentle 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. Miscellaneous Light Bulbs My 8" flourescent tube isn't the only light producer. Another classic u-oven experiment is to cook a standard lamp bulb briefly on "high". A 100W incandescent bulb will light up with more than normal brightness. Don't run this for very long, since ALL the lightbulb wires glow white hot, not just the filament wires. This could shatter the bulb. For best results, buy a transparant bulb rather than a frosted bulb, then watch what happens inside. There is an interesting bit of physics here: first the filament and its supporting wires glow white hot, but then they cool again. Bright blue beams leap between the tips of the filament supports and the glass, with bright "stars" of incandescence at the tips of the wires (many watts of Saint Elmo's Fire, like Nicola Tesla's 'carbon button' lamps!) This is a plasma discharge in the argon/nitrogen gas that is found inside all standard light bulbs. It's similar to Plasma Globe devices such as "eye of the storm", but 500 watts worth, which heats the glass red hot, and may melt the tips of the steel filament supports! Another one: elgersmad suggests trying xenon flash tubes. Note that most of these objects become intensely hot, so don't prop them up on a plastic object. And as usual, if this damages the microwave generator in your oven, don't come whining to ME! You know the risks, or you wouldn't be messing with this stuff. Go buy a huge old microwave oven for $5 at a garage sale, experiment with THAT.) 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 a "mu-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. The pattern is temporary, and disappears as the paper dries entirely. Also, cobalt chloride is poisonous, and should not be used around young kids. More recently, J. E. Slone of Virginia tells me that thermal FAX paper can be used for the same thing if is is slightly moistened. When placed on an insulating plate within the microwave oven, the hotspots heat the water to boiling which creates a permanent image of the standing wave pattern. Kool! Both of the above experiments will only work if your oven lacks a "stirrer," a fan which wiggles the hotspots and spreads them out. If your oven has a rotating turntable, it usually lacks a stirrer. Untried experiments Generate a glob of soot from burning paint thinner. Replace the air within the soot ball with pure oxygen, or ozone, or nitrogen, or argon. Place it within an active microwave oven. Is a Ball Lightning plasmoid created? Light a candle and place it in the oven. Does the RF energy make the candle flame grow huge? If you place various metal salts on the wick, will the colored candle flame absorb RF energy better? Or, try running a wire up through the candle so its tip is in the flame. Any effects? There are reports of "ball lightning" being generated from candles, burning toothpicks, and burning plastic in Microwave Ovens. Partially inflate a balloon with argon. Release the argon to purge the bit of air that was in the balloon, then fill it with pure argon. Carefully insert a wire up into the balloon so the wire tip is near the center of the sphere. Tie off the balloon. Place it on a plate in a microwave oven and turn it on. This should create a 700 watt "plasma ball" effect. However, it might also pop the balloon instantly. The tip of the wire will probably be melted by the intense corona. Anyone for "Kirlian photography" which vaporizes the object being photographed? If the balloon pops instantly, try the same thing by using a plexiglas box. (note: glue fumes wreck the effect, so hold the plexiglas together with tape.) Try the infamous Microwave Powered Water-Fueled Lawn Mower. Do huge pulses of EM really extract energy from a mysterious source within water? Dr. Graneau says that high current discharge through liquid water produces numerous anomalies. Laugh if you wish, but only the real world can supply the real answer. "Let the experiment be Made!" More and weirder experiments ------------------------------------------------------------------------ Other microwave oven sites on the WWW: Microwave oven Ball Lightning * Microwave Phenomenon Page * MW Oven Ball Lightning messages * Ball Lightning page * More Microwave BL * Abstract: Golka1.html from Atmospheric Electricity Page * Microwave oven BL, from Keelynet Misc sites * Glubco, far more "unwise" than I! * Fun with Grapes - A Case Study * Grape Racing! * T.W.I.N.K.I.E.S. Radiation Test * CD-ROM's in the Microwave * Microwave Oven Q & A at HOW THINGS WORK * Microwave Acoustics, w/refs on microwave hearing * Microwave Oven info, FAQs, repair * Microwave Ovens and Safety * Microwave Oven Reaction Enhanced Chemistry * Microwave Oven * Microwave Oven Radiation Leakage * Microwave Furnace Development * EEED Medical Technology ------------------------------------------------------------------------ Some Microwave Oven Myths Q: Do Microwave Ovens cook from the inside out? A: 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. Usually 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. This effect is different for different foods of course. If a food is mostly water, only the outside inch cooks at all. If a food contains both air and water (like bread, cake, etc.,) then the radio energy penetrates all the way through, and the food gets heated everywhere, even deep inside. Q: If I put a fork in the Microwave, will it destroy the oven? A: Nope, this is a myth, but it has some roots in reality. In order to safely use metals inside a microwave oven, the cook has 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. The staple heats up and sets fire to the bag. If a metal object in the oven is lightly touched to another one, or touched to the metal wall of the oven, an electric arc might ignite at the contact point. If not stopped it can set fire to the oven. Sharp points on metal objects 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. The alternative would be to send everyone to school to learn the complicated rules! Q: Aren't these ovens tuned to a special frequency so they only heat water? A: 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 this causes 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 rotates (vibrates) the water molecules (and any other polar molecules) within the food. Microwave ovens have difficulty melting ice, presumably because the water molecules are bound together and cannot be easily rotated by the e-fields. If the oven was tuned to the water resonance frequency, then the water would become far more opaque to the wave energy. The water in the food's thin surface would absorb all the energy, and only the outside surface of foods would be heated. The thin outer surface of meat would become a blast of steam, and the inside would remain ice cold. But because water does not resonate with the microwave frequency, the waves can travel an inch or so into the meat before being absorbed. Q: How to they work? A: OK, this question doesn't involve microwave oven myths, so I guess this section is becoming a FAQ. Microwave ovens are weird, they were born in a military "black project" dealing with exotic physics. The "magnetron" vacuum tube had its birth in England during World War II, and was the central part of a new secret weapon: radar. Eventually the secret military technology was declassified, and it ended up in appliance stores everywhere. One is led to wonder how many other incredible discoveries are still sitting unused in that (perhaps) non-mythical government warehouse seen briefly at the end of the first Indiana Jones movie! The Klystron and Magnetron microwave tubes both rely on nonlinear effects of density waves in particle streams interacting with solid surfaces and tuned cavities. That's right, they are identical to that bizarre resonant-cavity standing wave generator known as the EMPTY BEER BOTTLE. A microwave oven is like a whistle. Blow across a bottle orifice, and tiny sound waves within the bottle will cause the air jet from your lips to move slightly. Motions of the air jet create pressure waves in the bottle. Pressure waves wiggle the jet even more. Runaway feedback takes place, and a loud sound is created. If we replace the air with an electron stream in a vacuum, and use a hollow metal bottle, then radio waves will build up in the bottle as they deflect the electron stream back and forth. A microwave tube is an electronic whistle which creates a loud "sound" in the form of radio waves. Intense sounds can heat objects, and intense radio waves do the same. If we get our electron-whistle operating and then we try to extract energy, the resonance is ruined and only a little wave energy comes out. This problem was solved by using multiple "bottles" and a magnet to direct the electron stream across their "mouths". A magnetron tube consists of a centra electron emitter, one or two magnets which cause the electrons to swirl in a whirlpool motion, several tuned cavities with open mouths pointed into the whirlpool of charges, and a high voltage power supply which moves the electrons along at high velocity. Energy is extracted from just one of the tuned cavities, and this has only a small effect on the resonance of the others. If you wanted to create an acoustic model of a microwave oven, you could attach a vacuum cleaner to the center of a heavy cylindrical box. Put slots around the edge of the box. The resulting tornado acts to supply the jet of high-speed air. Several glass bottles could then be poked through the sides of the box, inserted into the tornado, and adjusted to give a loud tone. With luck, you might even be able to connect an "exit tube" to one of the bottles, connect the tube to a sealed metal cabinet, then actually heat any objects which are placed in the cabinet. Use really thick, heavy construction materials, otherwise the intense sound would not stay trapped inside your beerbottle-tron device. It would sound like an air-raid siren. The speed of light is about one million times faster than the speed of sound. However, the wavelength of the above sounds waves would be similar to microwave wavelength. So instead of giving out 1,000 MHz microwave radiation, your device would give out 1,000 Hz acoustical radiation (but with the same wavelength as microwave energy.) ------------------------------------------------------------------------ Please leave COMMENTS! Created and maintained by Bill Beaty. Mail me at: billb@eskimo.com. If you are using Lynx, type "c" to email.