A microwave oven is a kitchen appliance employing microwave radiation primarily to cooking or heat food. == History == The idea for using microwaves to cook food was discovered by Percy Spencer who was working for Raytheon and was building magnetrons for radar sets. One day he was working on an active radar set when he had noticed a sudden and strange sensation, and saw that a chocolate bar he had in his pocket had melted. The holder of 120 patents, Spencer was no stranger to discovery and experiment, and realized what was happening. The first food to be deliberately cooked with microwaves was popcorn, and the second was an egg (which exploded in the face of one of the experimenters). In 1946 Raytheon patented the microwave cooking process and in 1947, they built the first commercial microwave oven, the Radarange. It was almost 6 feet (1.8 m) tall and weighed 750 pounds (340 kg). It was water-cooled and produced 3000 watts, about three times the amount of radiation produced by microwave ovens today. This first step was so successful that Raytheon eventually purchased Amana to round-out a complete home appliance product suite. A number of other companies joined in the market, and for a time most systems were built by defense contractors, who were the most familiar with the magnetron. Litton was particularly well known in the restaurant business. By the late 1970s the technology had improved to the point where prices were falling rapidly. Formerly found only in large industrial applications, microwaves were increasingly becoming a standard fixture of most (western) kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use. By the late 1980s they were almost universal and currently it is estimated that nearly 95% of American households have a microwave. == Description == A microwave oven consists of: * a magnetron, * a magnetron control circuit (usually with a microcontroller), * a waveguide, and * a cooking chamber A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food. water (molecule), fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating. Most molecules are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and is therefore twisted to and fro as it tries to align itself with the alternating electric field induced by the microwave beam. This molecular movement creates heat. Microwave heating is most efficient on liquid water, and much less so on fats, sugars, and frozen water. Microwave heating is sometimes incorrectly explained as resonance of water molecules, but this occurs only at much higher frequencies, in the tens of gigahertz. The cooking chamber itself is a Faraday cage enclosure to prevent the microwaves escaping into the surroundings. The oven door is usually a glass panel, but has a layer of conductive mesh to maintain the shielding. Since the mesh width is much less than the wavelength of 12 cm, the microwave radiation can not pass through the door, while visible light (with a much shorter wavelength) can. Professional chefs generally find microwave ovens to be of limited usefulness. See Microwaving for a discussion of this reason. With wireless computer networks gaining in popularity, microwave interference has become a concern among those with wireless networks. Microwave ovens are capable of disrupting wireless network transmissions due to the fact that the microwave creates radio waves at about 2450 MHz. This is about the same frequency that wireless networks use, so microwave ovens in use can interfere with network signals and cause connection issues. ==Efficiency== A microwave oven does not convert all electrical energy into microwaves. A typical consumer microwave oven could consume 1100 W, and deliver 700 W of microwave power. The remaining 400 W are dissipated as heat by components of the oven. The main source of energy loss is the magnetron tube which is much less than 100% efficient at generating microwave output from the power source. Lesser amounts of power are consumed by the oven lamp, AC power transformer losses, magnetron cooling fan, food turntable motor and control circuits. This waste heat does not end up in the food but is mostly expelled from the cooling vents on the oven and heats the air in the kitchen . See Electrical efficiency. Most of the actual microwave power will end up heating the food inside the oven, unless the microwave oven is loaded with a very small amount of absorbing food. In that case, the magnetron element will reabsorb the microwaves, which can lead to overheating. ==Safety and controversy== Microwaving food is fast and popular, but there are potential hazards. See also: Microwaving. ===Uneven heating=== Food is heated for so short a time that it is often cooked unevenly. Microwave ovens are frequently used for reheating previously cooked food, and bacteriuml contamination may not be killed by the reheating, resulting in foodborne illness. The uneven heating is partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food. The first problem is reduced by a stirrer, a type of fan that reflection microwave energy to different parts of the oven as it rotates, and by a turntable that turns the food. The second problem must be addressed by the cook, who should arrange the food so that it absorbs energy evenly, and periodically test and shield any parts of the food that overheat. ===Acute dangers=== Distilled water, when heated in a microwave oven in a container with a smooth surface, can superheating, that is, reach temperatures that are a few degrees Celsius above the normal boiling point, without actually boiling. The boiling process can start steam explosion when the water is disturbed, such as when the operator grabs hold of the container to take it out of the oven, which can result in severe burns. Closed containers and eggs can explode when heated in a microwave oven due to the pressure build-up of steam. Products that are heated too long can catch fire. Manuals of microwave ovens typically warn of these hazards. Tin foil, aluminium foil, ceramics decorated with metal, and products containing other metals can cause sparks when they are cooked in a microwave (some find it entertaining to place a compact disc in a microwave for this reason, however this may produce toxic fumes, not to mention destroying the CD in a circular mesh pattern). ===Controversial hazards=== ====Food==== There exists an anti-microwave lobby that claims that there exist more subtle dangers than the ones listed above associated with cooking in a microwave oven. It is claimed that microwave cooking causes more loss of nutrients than conventional cooking and that microwave radiation leads to chemical reactions in the food that are different from those occurring during conventional heating. There is no accepted scientific validity to these claims and they are looked upon by scientists and skeptics in general as being alarmist and pseudoscientific to the point of ridiculousness. These issues are presented, in a one-sided fashion, in the following websites: *[http://www.relfe.com/microwave.html Microwave Cooking is Killing You!] *[http://www.mercola.com/2003/nov/5/microwave_food.htm Do You Microwave Your Food?] ====Radiation==== Some people are concerned with being exposed to the microwave radiation. The USA legal limit of leaking radiation is 1 mW/cm2 at 5 cm from a new oven (for a used oven, it is 5 times higher). It is rare for an oven to exceed these limits. As a comparison, a GSM cellular telephone may emit up to 1 W at 1800 MHz, which is 2 mW/cm2 at 5 cm. Whether or not cellular phones are hazardous to the health is also controversial. It is a common myth that metallic kitchen equipment, like kitchen forks and knives, can somehow repel the microwaves back into the magnetron and cause it to catch fire and maybe even explode. This is pure fantasy and is not to be taken seriously. ==See also== *Microwave meal == External links == * -- ''Method of treating foodstuff'' *[http://hps.org/hpspublications/articles/microwaveoven.html Health physics society: microwave oven safety] * [http://www.colorado.edu/physics/2000/microwaves How Microwaves Work] Article by Professor Lee, Colorado University * [http://www.gallawa.com/microtech/how_work.html How Microwaves Work] Article by Microtech * [http://everist.org/special/mw_oven/ "Fun Things to Do with Microwave Ovens"] by Guy Dunphy Electro mechanical engineering Home appliances fa:تندپز
Is there any data on the efficiency of firstly a magnetron and secondly the efficiency of food heating? :http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_009 says (without explanation) that magnetron efficiency is about 75% and oven efficiency is 50% to 60%. This ignores other factors, such as the ability to boil a single cup of water without having to heat a whole pan. -- User:Heron ==POV?== The second half of point 2 and point 4 of the hazard list sound like attempts to scare people. See for example the phrase: ''"Microwaved food contains both molecules and energies not present in food cooked in the way humans have been cooking food since the discovery of fire..."''. That is not a scientific argument to assess the safety of microwaved food. The point about energies is utter nonsense. The point of the molecules sounds dramatic, but in fact, every new vegetable contains hundreds of chemical compounds that are not present elsewhere. And this phrase: ''All foods that were processed through the microwave ovens caused changes in the blood of the volunteers.''. It is not claimed that the changes were larger or more dangerous than after consumption of other foods. What happened to Hertel is not nice, but "freedom of expression" is an issue different from "scientifically correct". I have removed most of the scare talk and replaced it with (I believe) a short NPOV paragraph. -- User:Hankwang 12:25, 17 Mar 2004 (UTC) The frequency range used by microwave ovens is same as that used by wireless devices operating in the ISM band. Why doesn't everyone get 'cooked'? -- User:heavy_chariot :A microwave oven pumps out several hundred watts of power, but the regulations for the ISM band limit the transmitter power to about 100 milliwatts per device, which is several thousand times less, and not all of that power is absorbed by the human body. Standing close to an ISM transmission does indeed heat you up, but only by a small fraction of one degree, and certainly not enough to cook you. -- User:Heron 11:03, 9 Apr 2004 (UTC) There is another reason that ISM phones don't cook, while microwaves do. Microwaves set up standing waves inside the metal cabinet, which amplify each other and can far exceed the power of the microwave. (a 1kw microwave could easily set up a 10kw standing wave- it would only take 10 cycles, which would happen in the blink of an eye). An ISM phone radiates, and no standing waves are set up in you head. So they are generally safe. == Arching == Does anyone know sufficient enough information on arching? I really want to learn more about it, but there doesn't seem to be too many resources on it. Anybody want to make a page in wikipedia? ;) How about corona discharge, electric arc, electrostatic discharge, electrical breakdown--User:Wjbeaty 18:20, Mar 4, 2005 (UTC) == Marvin Bock == This article credits Percy Spencer with the invention of microwave cooking, although I have heard accounts that a technician called Marvin Bock who worked for him should be given more credit for this. It seems unlikely that it would take 5 years between the invention of the cavity magnetron (in 1940), and its subsequent widespread production and use in WWII, and the discovery of its effect on matter containing water in 1945/46..... == Marvin Bock == My dear father, Marvin J. Bock (1914-1971) was an electrical engineer in Percy Spencer's R&D laboratory at Raytheon, and did indeed participate in the development of the microwave oven during the 1940s. In September 1984, Dr. John M. Osepchuk published "A History of Microwave Heating Applications" in the IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-32, No. 9. Page 1205 of that publication states, in para. 2: "Enthused Raytheon management sponsored a contest for a name for the microwave oven and the Radarange (TM) was born. Marvin Bock, who later worked with Tom Philips, today's CEO, built the first radarange, the Model 1132, which provided an output power of 1.6 kW from one water-cooled, permanent-magnet magnetron. This is shown in Fig. 3. Note that it was a free standing white-enameled unit operating from 220 V." Mr. Bock held five U.S. patents, including one related to microwave heating: #2,516,503 issued in 1950 and titled "Controlling Device for Cooking Apparatus". It discloses a means for shutting off microwave power when a food load is not present in a microwave cooking system. [Peter A. Bock (1942- )]
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Words begining with Microwave_oven:
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Microwave_oven
Microwave_ovens
Microwave oven
A microwave oven is a kitchen appliance employing microwave radiation primarily to cooking or heat food. == History == The idea for using microwaves to cook food was discovered by Percy Spencer who was working for Raytheon and was building magnetrons for radar sets. One day he was working on an active radar set when he had noticed a sudden and strange sensation, and saw that a chocolate bar he had in his pocket had melted. The holder of 120 patents, Spencer was no stranger to discovery and experiment, and realized what was happening. The first food to be deliberately cooked with microwaves was popcorn, and the second was an egg (which exploded in the face of one of the experimenters). In 1946 Raytheon patented the microwave cooking process and in 1947, they built the first commercial microwave oven, the Radarange. It was almost 6 feet (1.8 m) tall and weighed 750 pounds (340 kg). It was water-cooled and produced 3000 watts, about three times the amount of radiation produced by microwave ovens today. This first step was so successful that Raytheon eventually purchased Amana to round-out a complete home appliance product suite. A number of other companies joined in the market, and for a time most systems were built by defense contractors, who were the most familiar with the magnetron. Litton was particularly well known in the restaurant business. By the late 1970s the technology had improved to the point where prices were falling rapidly. Formerly found only in large industrial applications, microwaves were increasingly becoming a standard fixture of most (western) kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use. By the late 1980s they were almost universal and currently it is estimated that nearly 95% of American households have a microwave. == Description == A microwave oven consists of: * a magnetron, * a magnetron control circuit (usually with a microcontroller), * a waveguide, and * a cooking chamber A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food. water (molecule), fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating. Most molecules are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and is therefore twisted to and fro as it tries to align itself with the alternating electric field induced by the microwave beam. This molecular movement creates heat. Microwave heating is most efficient on liquid water, and much less so on fats, sugars, and frozen water. Microwave heating is sometimes incorrectly explained as resonance of water molecules, but this occurs only at much higher frequencies, in the tens of gigahertz. The cooking chamber itself is a Faraday cage enclosure to prevent the microwaves escaping into the surroundings. The oven door is usually a glass panel, but has a layer of conductive mesh to maintain the shielding. Since the mesh width is much less than the wavelength of 12 cm, the microwave radiation can not pass through the door, while visible light (with a much shorter wavelength) can. Professional chefs generally find microwave ovens to be of limited usefulness. See Microwaving for a discussion of this reason. With wireless computer networks gaining in popularity, microwave interference has become a concern among those with wireless networks. Microwave ovens are capable of disrupting wireless network transmissions due to the fact that the microwave creates radio waves at about 2450 MHz. This is about the same frequency that wireless networks use, so microwave ovens in use can interfere with network signals and cause connection issues. ==Efficiency== A microwave oven does not convert all electrical energy into microwaves. A typical consumer microwave oven could consume 1100 W, and deliver 700 W of microwave power. The remaining 400 W are dissipated as heat by components of the oven. The main source of energy loss is the magnetron tube which is much less than 100% efficient at generating microwave output from the power source. Lesser amounts of power are consumed by the oven lamp, AC power transformer losses, magnetron cooling fan, food turntable motor and control circuits. This waste heat does not end up in the food but is mostly expelled from the cooling vents on the oven and heats the air in the kitchen . See Electrical efficiency. Most of the actual microwave power will end up heating the food inside the oven, unless the microwave oven is loaded with a very small amount of absorbing food. In that case, the magnetron element will reabsorb the microwaves, which can lead to overheating. ==Safety and controversy== Microwaving food is fast and popular, but there are potential hazards. See also: Microwaving. ===Uneven heating=== Food is heated for so short a time that it is often cooked unevenly. Microwave ovens are frequently used for reheating previously cooked food, and bacteriuml contamination may not be killed by the reheating, resulting in foodborne illness. The uneven heating is partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food. The first problem is reduced by a stirrer, a type of fan that reflection microwave energy to different parts of the oven as it rotates, and by a turntable that turns the food. The second problem must be addressed by the cook, who should arrange the food so that it absorbs energy evenly, and periodically test and shield any parts of the food that overheat. ===Acute dangers=== Distilled water, when heated in a microwave oven in a container with a smooth surface, can superheating, that is, reach temperatures that are a few degrees Celsius above the normal boiling point, without actually boiling. The boiling process can start steam explosion when the water is disturbed, such as when the operator grabs hold of the container to take it out of the oven, which can result in severe burns. Closed containers and eggs can explode when heated in a microwave oven due to the pressure build-up of steam. Products that are heated too long can catch fire. Manuals of microwave ovens typically warn of these hazards. Tin foil, aluminium foil, ceramics decorated with metal, and products containing other metals can cause sparks when they are cooked in a microwave (some find it entertaining to place a compact disc in a microwave for this reason, however this may produce toxic fumes, not to mention destroying the CD in a circular mesh pattern). ===Controversial hazards=== ====Food==== There exists an anti-microwave lobby that claims that there exist more subtle dangers than the ones listed above associated with cooking in a microwave oven. It is claimed that microwave cooking causes more loss of nutrients than conventional cooking and that microwave radiation leads to chemical reactions in the food that are different from those occurring during conventional heating. There is no accepted scientific validity to these claims and they are looked upon by scientists and skeptics in general as being alarmist and pseudoscientific to the point of ridiculousness. These issues are presented, in a one-sided fashion, in the following websites: *[http://www.relfe.com/microwave.html Microwave Cooking is Killing You!] *[http://www.mercola.com/2003/nov/5/microwave_food.htm Do You Microwave Your Food?] ====Radiation==== Some people are concerned with being exposed to the microwave radiation. The USA legal limit of leaking radiation is 1 mW/cm2 at 5 cm from a new oven (for a used oven, it is 5 times higher). It is rare for an oven to exceed these limits. As a comparison, a GSM cellular telephone may emit up to 1 W at 1800 MHz, which is 2 mW/cm2 at 5 cm. Whether or not cellular phones are hazardous to the health is also controversial. It is a common myth that metallic kitchen equipment, like kitchen forks and knives, can somehow repel the microwaves back into the magnetron and cause it to catch fire and maybe even explode. This is pure fantasy and is not to be taken seriously. ==See also== *Microwave meal == External links == * -- ''Method of treating foodstuff'' *[http://hps.org/hpspublications/articles/microwaveoven.html Health physics society: microwave oven safety] * [http://www.colorado.edu/physics/2000/microwaves How Microwaves Work] Article by Professor Lee, Colorado University * [http://www.gallawa.com/microtech/how_work.html How Microwaves Work] Article by Microtech * [http://everist.org/special/mw_oven/ "Fun Things to Do with Microwave Ovens"] by Guy Dunphy Electro mechanical engineering Home appliances fa:تندپز
Microwave oven
Is there any data on the efficiency of firstly a magnetron and secondly the efficiency of food heating? :http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_009 says (without explanation) that magnetron efficiency is about 75% and oven efficiency is 50% to 60%. This ignores other factors, such as the ability to boil a single cup of water without having to heat a whole pan. -- User:Heron ==POV?== The second half of point 2 and point 4 of the hazard list sound like attempts to scare people. See for example the phrase: ''"Microwaved food contains both molecules and energies not present in food cooked in the way humans have been cooking food since the discovery of fire..."''. That is not a scientific argument to assess the safety of microwaved food. The point about energies is utter nonsense. The point of the molecules sounds dramatic, but in fact, every new vegetable contains hundreds of chemical compounds that are not present elsewhere. And this phrase: ''All foods that were processed through the microwave ovens caused changes in the blood of the volunteers.''. It is not claimed that the changes were larger or more dangerous than after consumption of other foods. What happened to Hertel is not nice, but "freedom of expression" is an issue different from "scientifically correct". I have removed most of the scare talk and replaced it with (I believe) a short NPOV paragraph. -- User:Hankwang 12:25, 17 Mar 2004 (UTC) The frequency range used by microwave ovens is same as that used by wireless devices operating in the ISM band. Why doesn't everyone get 'cooked'? -- User:heavy_chariot :A microwave oven pumps out several hundred watts of power, but the regulations for the ISM band limit the transmitter power to about 100 milliwatts per device, which is several thousand times less, and not all of that power is absorbed by the human body. Standing close to an ISM transmission does indeed heat you up, but only by a small fraction of one degree, and certainly not enough to cook you. -- User:Heron 11:03, 9 Apr 2004 (UTC) There is another reason that ISM phones don't cook, while microwaves do. Microwaves set up standing waves inside the metal cabinet, which amplify each other and can far exceed the power of the microwave. (a 1kw microwave could easily set up a 10kw standing wave- it would only take 10 cycles, which would happen in the blink of an eye). An ISM phone radiates, and no standing waves are set up in you head. So they are generally safe. == Arching == Does anyone know sufficient enough information on arching? I really want to learn more about it, but there doesn't seem to be too many resources on it. Anybody want to make a page in wikipedia? ;) How about corona discharge, electric arc, electrostatic discharge, electrical breakdown--User:Wjbeaty 18:20, Mar 4, 2005 (UTC) == Marvin Bock == This article credits Percy Spencer with the invention of microwave cooking, although I have heard accounts that a technician called Marvin Bock who worked for him should be given more credit for this. It seems unlikely that it would take 5 years between the invention of the cavity magnetron (in 1940), and its subsequent widespread production and use in WWII, and the discovery of its effect on matter containing water in 1945/46..... == Marvin Bock == My dear father, Marvin J. Bock (1914-1971) was an electrical engineer in Percy Spencer's R&D laboratory at Raytheon, and did indeed participate in the development of the microwave oven during the 1940s. In September 1984, Dr. John M. Osepchuk published "A History of Microwave Heating Applications" in the IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-32, No. 9. Page 1205 of that publication states, in para. 2: "Enthused Raytheon management sponsored a contest for a name for the microwave oven and the Radarange (TM) was born. Marvin Bock, who later worked with Tom Philips, today's CEO, built the first radarange, the Model 1132, which provided an output power of 1.6 kW from one water-cooled, permanent-magnet magnetron. This is shown in Fig. 3. Note that it was a free standing white-enameled unit operating from 220 V." Mr. Bock held five U.S. patents, including one related to microwave heating: #2,516,503 issued in 1950 and titled "Controlling Device for Cooking Apparatus". It discloses a means for shutting off microwave power when a food load is not present in a microwave cooking system. [Peter A. Bock (1942- )]
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