Why is it bad to put metalic objects in the microwave?
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The previous answers explain what metals DO in the microwave, but not WHY.  \n\nIt is not necessarily bad that metal is in the microwave: the walls of the microwave are made of metal!  What is so special about metal?\n\nThe reason that metals are shiny is that they have free electrons in them.  The free electrons in metal are what make the metal electrically and thermally conductive; ceramics don't have free-electrons and so are not shiny- metallic in appearance (you can tell just by looking).\n\nIt turns out that the free electrons in the metal reflect photons (energy packets) of light for both visible and thermal (microwave) ranges.  Long electromagnetic waves (microwaves) also behave as photons; we don't call them photons of light because we can't see them, but microwave photons are in fact the same kind of photon, just of lower energy.  It is important to understand that all that is going on in the microwave is that the metal in the microwave is reflecting the microwaves (and not being absorbed).\n\nThe way that microwave heat is by coupling electromagentically to 'wiggle' atoms (certain atoms/molecules anyway; those that have a dipole moment) very fast, causing heating (not metals of course - the microwaves bounce off; and not materials without a dipole moment, which is why some ceramics and glasses don't heat up).  Water isn't even the most efficient coupling material at microwave frequencies; this is why sugar heats up so much faster. \n\nThe microwaves are reflected by the metal walls until they are absorbed, (usually by water-containing food), their energy being converted to heat. Should absorption not take place - if, for example, the oven is activated when empty, some energy will re-enter the waveguide and cause over-heating of the magnetron. Usually a safety switch turns the machine off when this happens. Note that the reflecting walls and the constant frequency of the microwaves set up standing waves in the chamber. This results in some areas being much more active than others and is the reason why food must be rotated through the varying field to cook evenly.  \n\nSo why does a metallic fork arc?  The resonance induces enough movement in the electrons in the metal to create an electric field charge sufficient to arc (even though it is a reflecting material, electrical currents are induced).  Note that the metal object won't arc if it is grounded to the walls, and it won't arc if it is insulated sufficiently (I have a metal 'roast rack' in my microwave).\n\nGenerally it is not a good idea to put metals in the microwave because you want the food to absorb the energy, the manufacturer of the microwave spent a lot of time designing the standing wave energy field to be uniform to do just that, and introducing metal distorts that field - its OK if you know what you're doing, not so good if you don't have a purpose in mind.
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The website TruthorFiction decided this is not true.\n\n"Don't Use Plastic for Heating Foods in a Microwave Oven Because of Exposure to Dioxins-Unproven! & Fiction!"\n\nThis site does an exhaustive investigation regarding "rumors" put out there.  You can read how they came to this conclusion at the following site:\n\nhttp://www.truthorfiction.com/rumors/d/dioxins.htm
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I've heard of people claiming you can smelt aluminum, etc., in a microwave oven, if you use silica bricks to contain the heat. You might also need to use a graphite crucible, which will heat up but that the molten metal will not stick to. \n\nFinally, since magnesium is SO flammable (but that's why you want to smelt it, to make inconspicuous incendiary devices, right? you dirty little terrorist) you need to have a continuous stream of some non-oxidizing gas, such as nitrogen, flowing through the oven while it is in use.\n\nBottom line? Don't try this at home. You'll get yourself killed if you're lucky, burned and crippled for life if you're not. And I'm asking the yahoo people to contact the local law enforcement authorities in your area.
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A microwave makes food hot by causing the protons and electrons in the food move about quickly.  The microscopic particles in a regular plate won't move as quickly as the ones in the food and therefore, won't get hot as fast.  Metal, on the other hand, has microscopic particles which start reacting to the microwave energy very quickly.  These little bundles of energy start moving so fast that they begin sparking in your microwave oven.  This is why you can't put aluminum foil in your microwave and also why you can't cook in the microwave with gold trimmed plates.
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You have the potential for galvanic corrosion.  Essentially, two metals at different potentials share electrons and one metal (the one with the higher potential) will start to erode and "plate" the other metal.\n\nTypically, using some sort of material that is a non-conductor (ceramics, rubber, etc) between the two or passivating the metal surfaces or coating the metal surfaces (prime and paint per ANSI standards) are your best options to prevent this.
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Metal does not return radiation back to the magnetron. The problem is that the metal, being highly conductive, acts as an antenna element, and thus builds up electric charge. This is less of a problem with non-pointed objects, as those are the objects that can cause dangerous sparks as the charge is greater at the points. \nAlso, since the metal is acting as a resistor, it is building up a lot of heat, which is dangerous to non-metallic objects that may be in contact with it. \nSee the article below for more information.
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The microwaves hae a frequency which is very close to the distance between the Hydrogen and Oxygen atoms in the water molecule. Because of this fact it causes that bond to vibrate and thereby adding energy or heat. This is why water is required for a microwave.
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Microwave oven cannot operate with the door open, unless tampered with, and then they are dangerous to anyone around them.  Given that the magnetron is a sensitive component, and that it operates at high voltage, tempering with it can be deadly to whoever is doing it unless they know what they are doing (i.e. they are expert in the field, like electrical enginners or technicians)\nThe door prevents microwaves from going out because it contains a metallic mesh forming a Faraday cage with the rest of the metallic enclosure.  That means if you were to put a screen mesh on your ceiling -- a mesh with a pitch similar to that used in mircowave doors (visible in the window) or smaller, no microwave would be able to get through.\nMicrowaves are absorbed by stuff that contains water, which is how food gets warmed up.  If your ceiling is plaster, it contains water in fixed form; if it was heated with microwaves, it would start flaking off.  If there is no dammage at all, then you only are the victim of a sick joke and idle threat and you will not come to any harm.
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The magnetic bars in most toys are coated with plastic.  The plastic is relatively inert in the stomach acid and passes through to the intestines.\n\nTwo magnets in the intestines can attract each other and cause either a perforation (hole in the intestines that leads to a severe infection) or an obstruction/blockage.  Either requires surgery to correct.
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********************************************************\n\nIf you ask me, one of the cleverest parts of a microwave oven is the door. It lets you see into the oven to make sure your potato isn't about to explode, yet keeps your face from being cooked off by microwaves in the process. It accomplishes this remarkable feat with a metal mesh—basically a sheet of metal with a regular pattern of small holes drilled or punched in it. This, along with the metal material of the oven cavity itself, forms a sort of reverse Faraday cage. A Faraday cage is a metal enclosure that normally keeps electrostatic fields and RF (radio frequency) radiation from getting in, but in the case of the oven, from getting out.\n\nA solid sheet of metal would be the most efficient at containing RF, but since you can't see through metal (unless you happen to be Superman), a compromise must be made. How much RF escapes through the mesh depends largely on two factors: the wavelength of the radiation in question, and the diameter of the holes. (For you picky types, the conductivity of the mesh material has a slight but negligible effect, as does the shape of the holes, among other things.) The shorter the wavelength of the RF, the smaller the holes need be to block the radiation. Microwave ovens operating at 2450 MHz emit radiation with a wavelength of about 12 centimeters, and the holes in the mesh of the door are typically on the order of 1-2 millimeters in diameter. Since the holes are small compared to the wavelength of the microwaves, little radiation can leak out. There are also mesh screens on the sides of the oven cavity, one to protect the oven light while allowing it to shine into the cavity, the other to permit ventilation.\n\nThe FDA has set emission standards for new microwave ovens at a power density of 5 milliwatts per square centimeter at a distance of 5 centimeters from any point on the outer surface of the oven. Typical new ovens have a leakage of only 0.2 mW/cm2 at that distance—a tenth of the FDA standard. Dirt, mechanical abuse and everyday wear and tear can eventually reduce the effectiveness of the door seals, thus increasing leakage. If you're concerned about emissions from an older oven, you can purchase leakage sensors at many hardware and home improvement stores or online. Keeping the seals on the oven and door clean, as well as opening and closing the door gently, will help keep your oven safe to use. So go ahead and ogle your latest culinary masterpiece while it cooks. Your food will cook, but your head will not. Or so one certainly hopes. \n\n**************************************************************
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Almost anything with an electric motor. (the starter on your car)\nElectric locks, relays (that clunk when you turn on the microwave)\nThe microwave itself (something called a magnetron inside which makes the radar waves that cook the food).
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what you do is you get 3 chunks of that foam stuff used for packing (not the peanuts the little bricks)\nmake sure they are about an inch thick.... alternatively you can use chunks of wood NO METALLIC OBJECTS!!!!!!!\n\nthen get your hands on a small clear vase or you can also use a big drinking GLASS\n\nset the blocks in your microwave, in a pattern that will let you set the glass upside down on the platter but you can still get your finger into the glass from the bottom.....\n\nlight a match and stick it directly under the glass...\n\n(the blocks help the match get air)\n\nset the microwave to high for 20 seconds.... you will see an awesome light show inside the glass, the glass will NOT be hot and will NOT explode, as well as your microwave will NOT be harmed\n BUT\n\nthere is a gas formed by this method of plasma creation...\nto us its poisonous, im not sure what it is exactly but dont breath it, it will not stay on items or taint items but if you BREATH it you can get sick.\n\nyou can choose to clean the glass and use it again and again and not have any problems as there was no residue to clean to begin with... or\nyou can just chuck it.\n\nalternatively you can just run over to spencer's gifts and pick up a plasma globe
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That's completely untrue! There is a microwave at almost anybody's house in Japan. It's very commonly used to heat food.\nThere are people who are concerned about the electromagnetic wave that a microwave releases while it's in use. I think it's same as a microwave in the states. (my mom tells me to stay away from the microwave while heating food! She's too conscious!!) This electromagnetic wave are in doubt that it could cause some damage in our brain. But it's not proved yet. And most people don't really care. \nSo everyone uses microwave for heating food in Japan! I'm sure of this.
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The microwave oven emitts a strong magnetic field when it operates. That magnetic field screws with sensitive electronics. Your detector may be sensitive to it.
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Microvaves are very short radio waves and will "transmit" through any hole you make in a microwave oven.  The waves can denature (cook) human flesh and are highly dangerous.  Even faulty door seals were a problem in early microwave ovens and it was feared they might ruin eye sight.  You should not alter any microwave oven unless you are a microwave engineer with special leak detection equipment.
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If you're talking about microwave ovens, the microwave heats up the water molecules in an egg, creating steam which builds up enough pressure to cause it to explode.
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One of the basic characteristics of microwave energy is that it is reflected by metal. The extent to which microwaves are reflected varies with the type of metal. For example, aluminum and stainless steel reflect microwaves, while certain compositions of cold-rolled steel will absorb microwave energy to some extent. However, for all practical purposes, it may be said that metal reflects microwave energy.\nThe characteristics of microwaves make it possible to contain them within a specially constructed metal enclosure called a cavity . The microwaves bounce around this  oven cavity until they are either absorbed by food or dissipate into the air. The interior metal walls of a microwave oven cooking cavity are proportioned with the energy output from the magnetron tube. In other words, the physical proportions of the cavity are tuned to the frequency of the energy, thus producing a uniform electromagnetic wave pattern. (The sealing properties of the door, which essentially appear as a metal wall to the microwaves, and the resonant characteristics of the oven cavity, will be considered in more depth in future additions). Therefore, under normal circumstances the energy reflects from wall to wall like beams of light in a mirrored room. However, if something were to disrupt that energy pattern, it would produce undesirable results, such as arcing.\nLike a Small Bolt of Lightning\nWhen metallic objects are indiscriminately placed in a microwave oven cooking cavity, the energy pattern becomes disrupted and distorted. This condition produces arcing. When two metal objects, such as a metal bowl and the [metal] cavity wall, are placed in close proximity and subjected to an intense field of microwave energy, arcing will result. Arcing in a microwave oven is like a small bolt of lightning Arcing occurs because the air between the two metallic objects becomes electrically charged, just as the air between a thundercloud and the earth becomes charged or ionized. This ionized air becomes an electrical conductor, and electric current then leaps the gap like a small bolt of lightning.