I'm finishing up my Biology quiz and my question is, "Explain why a microwave oven can heat foods?
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Why is this on a BIOLOGY quiz? It's a physics question.\n\nAnyway, the short answer is that microwaves are absorbed preferentilaly by certain materials, most commonly by water. Because most foods conatin water they can absorb the microwaves. The microwaves excite the water molecules producing heat and cooking the food.
880628
Hmm, the basic principle is that it excites the water molecules in food which creates heat energy. Don't know about putting a radioactive element in there...
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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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Microwaves and ocean waves share one common characteristic:\nIt is the transfer of energy through a medium.  The waves have a variable intensity.  For a microwave it is electromagnetic energy traveling at the speed of light with a frequency in the giga-hertz range.  For an ocean wave is the transfer of mechanical energy at a frequency of 1 per 30 seconds or so.  The height of the wave is proportional to the amount of energy and the depth of the water.\n\nIn the case of communications, the microwave energy is modulated to transmit information according to the modulation protocol and frequency.\n\nI hope that helps.\n\nBy the way, microwave energy is used in microwave ovens because the frequency of the microwave causes the water molecules in the food to react and heat.  This is because the water molecule is a bipolar molecule with a resonanat frequency that gets matched up to the microwave and thus converts the electromagnetic energy into kinetic energy, which gets converted to heat.\n\nj
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Percy Spencer discovered that microwaves could be used to cook when experimenting with magnetrons for radar at Raytheon.  I believe he accidentally melted a chocolate bar in his pocket and then went on to figure out how to use microwaves to heat food on purpose.
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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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Hello,A Micro Wave Oven Works On The Principle In Which It Uses Infrared Waves(Micro Waves), Which Make The Molecules Present In Food To Rotate in To n Fro Motion, And The Motion Is So Fast That It Heats Up The Food (The Food Molecules Move About Few Lakh Times In One Second) :-)
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Microwaves themselves were not invented; they are a kind of electromagnetic radiation, like light or radio waves. Percy Spencer invented the microwave oven while working for Raytheon.
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The microwave are a special high frequency radiation. To generate these waves, there is a device called Magnetron. The magnetron control circuit, as the name suggests, controls the magnetron for correct frequency locking and duration of radiation.
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convection microwaves have the capacity to brown food while cooking. eg:- the crust you see in baked dishes.\ngeneral microwaves may have most of the other features except browning. also convection feature means the oven will cost more. many don't use the convection feature inspite of it existing in the microwave so unless you are into major baking and roasting and hoping to get that perfect brown covering you can simply go in for a regular microwave its cheaper n has all the other features we require on a daily basis.
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Roaches are flat. The microwave radiation's electric field intensity falls to nearly zero as you approach the conducting inner wall. The oscillating E field is what heats water.
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Microwaves are shielded so that the energy doesn't get out. So, if the roach was on the outside it was as safe as you. \n\nThe energy is focused in the center of the microwave and absorbed quickly by anything there. A cockroach inside the microwave would get steamed a bit, but not too hot to survive.\n\nWhen the US government was testing nukes in the desert, they found cockroaches that survived the shockwave.
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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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Microwaves cause the water molecules in the food to vibrate rapidly making heat from the friction.  No harm if you don't tamper with the oven's seals etc.
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the microwave literally shoots microwaves at the food; these microwaves then vibrate the food particles, causing friction, which heats them up.\n\nhttp://www.gallawa.com/microtech/how_work.html how a microwave works, technically
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It is called the energy of activation or activation energy. The bacteria and maybe fungi cannot multiply at the reduced temps so the food will not be attacked by the microbes.Also proteins don't breakdown quickly at lower temps so the food will be fresh when it defrosts
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I think it's lack of mass.  microwaves are really short waves that pass through certain materials.  Will a microwave cook a single grain of rice?  That would confirm this. . .