MICROWAVE OVENA microwave oven creates radio waves at a frequency of about 2.45 GHz . Allradio waves are electromagnetic r...
plasma in the arc has a low resistance.The electrical resistance of foods can range from low to very high. Many foods will...
power instead of just cycling it between high and off.I decided to try microwaving some audio CDs to prove that the power ...
central cylindrical cathode within a thick cylinder that forms an anode shell. Along theinside of the shell are resonance ...
forces of the electric charge, together with the magnetic field, cause the electrons totravel in an ever-expanding circula...
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Microwave oven

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Microwave oven

  1. 1. MICROWAVE OVENA microwave oven creates radio waves at a frequency of about 2.45 GHz . Allradio waves are electromagnetic radiation.When a polar molecule is placed in an electric field, it lines up with that field. It issimilar to how a compass needle lines up with a magnetic field. Depending on thestrength of the electric field, it will even stretch the polar molecule. But it willspring back as soon as the electric field is removed. So, the way a microwaveworks is, the rapidly oscillating electric field causes the polar molecules to moveback and forth, increasing their kinetic energy (or heat). When matter is heated,the atoms and molecules start to vibrate faster. So far, it sounds like the heatfrom microwaves is no different than the stove. But there is one major difference.Microwaves have a strong electric field.Electromagnetic radiation is a self-propagating wave composed of twocomponents: an electric field, and a magnetic field. The two fields expand andcollapse as they propagate through space. As the electric field collapses, itproduces an expanding magnetic field. Conversely, as the magnetic fieldcollapses, it produces an expanding electric field [4]. This is a simple explanation,and there are more details involved.If the electric field is strong enough, not only will it stretch the molecule, it canalso separate the charges enough so that an atom loses an electron. This isionizing. Or it can separate a molecule. This is similar to electrolysis.When electricity flows in a conductor, free electrons drift easily in the direction ofthe electric field. In a non-conductive material, the electrons are tightly bound tothe atoms. If the electric field is strong enough, electricity will flow. The non-conductive material often gets destroyed when the electric field is strong enoughto ionize the atoms and force conduction, which creates a plasma such as a spark.A plasma is made of ionized atoms or molecules. A plasma can be formed in a gas,a solid, or even a liquid, but not in a pure vacuum. A plasma being formed in asolid is a foreign concept to some, but familiar to semiconductor physicists. Oncethe plasma is formed, the resistance drops very low and it conducts electricityeasily. This is why arc-welders dont need to use megawatt power supplies. The
  2. 2. plasma in the arc has a low resistance.The electrical resistance of foods can range from low to very high. Many foods willconduct some electricity when placed in an electric field. The electric field in themicrowave oven causes electric currents to flow in the food. This is similar towhat happens when an antenna picks up current from a radio wave.Electrical current can also rearrange atoms. For example, in microchips, the wireshave to be big enough or the force of the electrons actually can move enoughmetal so the wire distorts until it breaks [5].If electric current can rearrange metal, it can also rearrange the atoms in yourfood, changing the molecular structure. This happens either by ionization, or bymomentum transfer from the electron to the atom. This is one reason whynutrients can be destroyed more easily in a microwave oven than on the stove.Even though microwaves are classified as non-ionizing radiation, at sufficientpower levels, they can cause ionization such as a plasma [6, 7, 8].Despite the slang term nuke, microwaves are not nuclear radiation. Nuclearradiation consists of high speed alpha particles (helium nucleus), beta particles(high velocity electrons), neutrinos, gamma rays (extremely high energy photons),or high speed neutrons [9]. Nuclear radiation is classified as ionizing radiation [10]because it will ionize matter at any level of radiation. Every radioactive particlehas the potential to ionize when it interacts with matter.Ionizing, or simply displacing a single electron sounds harmless enough, but this isenough energy to destroy biological molecules. This is what kills every livingorganism that goes through the irradiation [11] process, including the food. Coldpasteurization (a nice name for irradiation) really is nuking your food.There is a tendency for most microwave users to cook everything on high power,except when defrosting. High is the default setting? The maximum power is also amajor selling point for a microwave oven. The higher the power, the stronger theelectric field and the more damaging it are to nutrients. So, lower the power, thesafer. But only some microwave ovens are capable of true low power cooking.The microwave ovens equipped with inverter magnetrons actually reduce the
  3. 3. power instead of just cycling it between high and off.I decided to try microwaving some audio CDs to prove that the power level had aneffect on the amount of damage done while cooking to the same temperature.Although it would be an honourable sacrifice in the name of science, rather thanuse my wifes Barry Mani low collection, I thought it would be more prudent toburn some songs onto identical CDs and experiment on those instead.I set my inverter-magnetron microwave to cook at 30% power for 3 1/2 minutes. Iplaced the CD in a plastic bowl and added 1 cup of water at 74°F. After cooking,the temperature was 158°F. I dried off the CD and stuck it in my CD player. It stillplayed. All 16 songs were still ok. I then placed a second, identical CD in the bowland again added 1 cup of water. I cooked it for one minute on high power. It wentfrom 73°F to 162°F, so it got approximately the same amount of heat. But the CDwas visibly much damaged. The CD player obviously couldnt even read it.Although this was a crude experiment, it illustrates the fact that cooking on highpower causes more damage than cooking on low power. So, the higher thepower, the more damage it causes, even if the final temperature is the same.It is a well-known fact that raw food is more nutritious than cooked. Cooking fooddestroys nutrients, whether its on a stove, or in the microwave oven. Butmicrowaving food on high power can be more destructive than cooking on thestove. So if you use a microwave, use one with an inverter magnetron, and cookon low power. Cooking on true low power (not intermittent high) will greatlyreduce the amount of damage done to the food.MAGNETRONDescriptionA magnetron is an electric device that produces microwave energy by convertingelectrical energy to radio frequency energy. It is commonly used as the heating elementin modern microwave ovens.ConstructionA magnetron is a type of diode, a special type of vacuum tube that converts low voltageelectrical energy to high voltage, then to radio frequency energy. A magnetron contains a
  4. 4. central cylindrical cathode within a thick cylinder that forms an anode shell. Along theinside of the shell are resonance chambers with openings. Top and bottom plates seal thecylinder, which is then placed within a powerful magnet.Energy Conversion ProcessWhen the cathode is heated, it gives off large amounts of negatively-charged electrons,which the positively-charged anode will attract. This process converts and steps up thelow-voltage AC current, used to heat the cathode, to high-voltage DC current that flowswithin the magnetron chamber.Microwave Generation and BroadcastThe flow of this current is controlled by the strong magnetic field. As the electrons flowwithin the vacuum, the resonance chambers within the walls of the anode emit very highfrequency energy in the form of a microwave field. This energy is then collected by anantenna and sent through a wave guide, a type of tube that directs it with little or no loss.The energy is then directed to another antenna that transmits the microwaves.The Life Force of the Microwave OvenThe magnetron is the life force of the microwave oven. A microwave oven works bysending microwaves of energy to the food, which causes the water content in the food toheat rapidly, thereby rapidly heating the food. In order for this to happen, a high-voltagesystem is necessary. The life force of this high-voltage system is the magnetron, whichuses a combination of electric and magnetic fields in order to create the microwaves that"bounce" around the microwave to heat the food.Internal Structure of the MagnetronA magnetron is made up of the following parts:* Anode/Plate: A hollow, iron cylinder that works with the cathode tocontrol the movement of the microwaved energy* Cathode/Filament: In combination with electrical current, thefilament emits electrons that travel between itself and the anode* Antenna: A probe that goes from the anode to the waveguide andhelps to guide the energy emitted from the magnetron* Magnetic Field: Created by strong magnets that are mountedaround the magnetron to create a magnetic field parallel to thecathodeHow the Magnetron WorksThe process begins when an electrical current is sent to the cathode/filament. The heatthat results from the electrical current causes an increase in molecular activity, therebyemitting electrons into the space between the cathode and anode. Both the cathode andthe electrons are negative charges; the anode is a positive charge. This results in theelectrons moving away from the cathode and toward the anode, at higher rates of speedas the temperature rises and causes more molecular activity.The electrons follow the antenna toward the anode. During this process, the electronsencounter the magnetic field, which detracts the electrons from their destination. The
  5. 5. forces of the electric charge, together with the magnetic field, cause the electrons totravel in an ever-expanding circular orbit until the electron finally reaches the anode.This circular motion of electrons is what produces the microwaves of energy that allowsfood to be rapidly heated within the contained space of the microwave oven.

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