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1. Microwave oven
1. Microwave oven

A microwave oven, or microwave, is a kitchen appliance that can come in many different sizes and styles employing microwave radiation primarily to cook or heat food. For the Banana Yashimoto novel see Kitchen (novel A kitchen, is a room or part of a room (sometimes called "kitchen Home appliances are electrical/mechanical Appliances which accomplish some Household functions such as Cooking or cleaning. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Cooking is the process of preparing Food by applying Heat, selecting measuring and combining of ingredients in an ordered procedure for producing safe and edible Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an This is accomplished by using microwaves, almost always emitted from a magnetron, to excite water (primarily) and other polarized molecules within the food to be heated. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a This excitation is fairly uniform, leading to food being heated everywhere all at once (except in thick objects), a feature not seen in any other heating technique.

Although microwave radiation in and of itself can be dangerous, when used properly these devices heat food quickly, efficiently, and safely.

Microwave ovens have revolutionized food preparation since their use became widespread in the 1970s. Food preparation is the act of preparing foodstuffs for consumption

Contents

History

Cooking food with microwaves was discovered by Percy Spencer while building magnetrons for radar sets at Raytheon. Percy Lebaron Spencer ( 9 July, 1894 – 8 September, 1970) was an American engineer and inventor A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Raytheon Company ( is a major American Defense contractor and industrial corporation with core Manufacturing concentrations in Defense systems He was working on an active radar set when he noticed that a peanut chocolate bar he had in his pocket started to melt. The peanut, or Groundnut ( Arachis hypogaea) is a species in the Legume family Fabaceae native to South America, Mexico The radar had melted his candy bar with microwaves. The first food to be deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters. Popcorn or popping corn is a type of corn which explodes from the kernel and puffs up when heated [1] To verify his theory, Spencer created a high density electromagnetic field by feeding microwave power into a metal box which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly.

On October 8, 1945 Raytheon filed a U. Events 314 - Roman Emperor Licinius is defeated by his colleague Constantine I at the Battle of Cibalae, and loses Year 1945 ( MCMXLV) was a Common year starting on Monday (link will display the full calendar S. patent for Spencer's microwave cooking process and an oven that heated food using microwave energy was placed in a Boston restaurant for testing. In 1947, the company built the Radarange, the first microwave in the World. [2]. It was almost 6 feet (1. 8 m) tall, weighed 750 pounds (340 kg) and cost about US$5000 each. It consumed 3 kilowatts, about three times as much as today's microwave ovens, and was water-cooled. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. An early commercial model introduced in 1954 consumed 1600 watts and sold for US$2,000 to US$3,000. Raytheon licensed its technology to the Tappan Stove company in 1952. They tried to market a large, 220 volt, wall unit as a home microwave oven in 1955 for a price of US$1,295, but it did not sell well. In 1965 Raytheon acquired Amana, which introduced the first popular home model, the countertop Radarange in 1967 at a price of US$495. The Amana Corporation was founded by George Foerstner as Amana Refrigeration in 1934 in Amana Iowa to manufacture commercial walk-in coolers

In the 1960s, Litton bought Studebaker's Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Named after inventor Charles Litton Sr, Litton Industries was a large defense contractor in the United States, bought by the Northrop Grumman Corporation Studebaker Corporation, or simply Studebaker, was a United States Wagon and Automobile manufacturer based in Litton then developed a new configuration of the microwave, the short, wide shape that is now common. The magnetron feed was also unique. This resulted in an oven that could survive a no-load condition indefinitely. The new oven was shown at a trade show in Chicago, and helped begin a rapid growth of the market for home microwave ovens. A trade fair (or trade show) is an exhibition organised so that companies in a specific Industry can showcase and demonstrate their latest products service study Chicago (ʃɪˈkɑːgoʊ is the largest City by population in the state of Illinois and the American Midwest of the United States. Sales volume of 40,000 units for the US industry in 1970 grew to one million by 1975. Market penetration in Japan, which had learned to build less expensive units by re-engineering a cheaper magnetron, was faster. For a topic outline on this subject see List of basic Japan topics.

Several 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, microwave ovens (often referred to informally as simply "microwaves") were increasingly becoming a standard fixture of most kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated By the late 1980s they were almost universal in the US and had taken off in many other parts of the globe. Current estimates hold that over 90% of American households have a microwave. [3]

Currently, the Chinese firm Galanz is the largest maker of microwave ovens in the world. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Galanz (Galanz Enterprise Group Co of Guangdong ( is a Chinese company and the largest producer of Microwave ovens in the world Annually the firm produces over 15 million appliances accounting for 40% of the global market.

Principles

2. Magnetron with section removed (magnet is not shown)
2. Magnetron with section removed (magnet is not shown)

A microwave oven consists of:

A microwave oven works by passing non-ionizing microwave radiation, usually at a frequency of 2. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A microcontroller (also MCU or µC is a functional Computer system-on-a- chip. In Electromagnetics and communications engineering, the term waveguide may refer to any linear structure that guides electromagnetic waves Non-ionizing radiation (or esp in British English, non-ionising radiation) refers to any type of Electromagnetic radiation that does not carry enough Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Frequency is a measure of the number of occurrences of a repeating event per unit Time. 45 GHz (a wavelength of 12. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. 24 cm), through the food. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Microwave radiation is between common radio and infrared frequencies. Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating. Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Dielectric heating (also known as electronic heating, RF heating, high-frequency heating) is the phenomenon in which Radiowave or Microwave Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Microwave heating is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate). Microwave heating is sometimes explained as a rotational resonance of water molecules, but this is incorrect: such resonance only occurs in water vapor at much higher frequencies, at about 20 gigahertz. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's For other meanings see Giga (disambiguation Giga- (symbol G is a prefix in the SI system of units denoting 109 The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Moreover, large industrial/commercial microwave ovens operating at the common large industrial-oven microwave heating frequency of 915 MHz (0. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. 915 GHz), also heat water and food perfectly well. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. [1] The frequencies used in microwave ovens were chosen based on two constraints. The first is that they should be in one of the ISM bands set aside for non-communication purposes. The industrial scientific and medical (ISM Radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial scientific and medical Three additional ISM bands exist in the microwave frequencies, but are not used for microwave cooking. The industrial scientific and medical (ISM Radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial scientific and medical Two of them are centered on 5. 8 GHz and 24. 125 GHz, but are not used for microwave cooking because of the very high cost of power generation at these frequencies. The third, centered on 433. 92 MHz, is a narrow band that would require expensive equipment to generate sufficient power without creating interference outside the band, and is only available in some countries. For household purposes, 2. 45 GHz has the advantage over 915 MHz in that 915 MHz is not an ISM band in all countries while 2. 45 GHz is available worldwide.

A common misconception is that microwave ovens cook food from the "inside out". In reality, microwaves are absorbed in the outer layers of food in a manner somewhat similar to heat from other methods. The misconception arises because microwaves penetrate dry non-conductive substances at the surfaces of many common foods, and thus often induce initial heat more deeply than other methods. Depending on water content, the depth of initial heat deposition may be several centimeters or more with microwave ovens, in contrast to broiling (infrared) or convection heating, which deposit heat thinly at the food surface. For the device used to cook see Grill (cooking, for other uses see Grill. Penetration depth of microwaves is dependent on food composition and the frequency, with lower microwave frequencies (longer wavelengths) penetrating better.

Most microwave ovens allow the user to choose between several power levels, including one or more defrosting levels. In most ovens, however, there is no change in the intensity of the microwave radiation; instead, the magnetron is turned on and off in duty cycles of several seconds at a time. In Telecommunications and Electronics, the term duty cycle is used to describe the fraction of time that a system is in an "active" state This can actually be observed when microwaving airy foods which may inflate during heating phases, and deflate when the magnetron is turned off. For such ovens, the magnetron is driven by a linear transformer which can only feasibly be switched completely on or off. Newer models have inverter power supplies which use pulse width modulation to provide truly continuous low-power microwave heating. Pulse-width modulation (PWM of a signal or power source involves the Modulation of its Duty cycle, to either convey information over a

The cooking chamber itself is a Faraday cage enclosure which prevents the microwaves from escaping into the environment. A Faraday cage or Faraday shield is an enclosure formed by conducting material, or by a mesh of such material The oven door is usually a glass panel for easy viewing, but has a layer of conductive mesh to maintain the shielding. Because the size of the perforations in the mesh is much less than the wavelength of 12 cm, most of the microwave radiation cannot pass through the door, while visible light (with a much shorter wavelength) can. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 With wireless computer networks gaining in popularity, microwave interference has become a concern near wireless networks. Wireless network refers to any type of Computer network that is Wireless, and is commonly associated with a Telecommunications network whose interconnections Microwave ovens are capable of disrupting wireless network transmissions because the ovens generate radio waves of about 2. 45 GHz in the 802.11b/g frequency band, some of them escaping the enclosure despite the presence of the mesh. Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used

Uses

Microwave ovens are generally used for time efficiency in both industrial applications such as restaurants and at home, rather than for cooking quality, although some modern recipes using microwave ovens rival recipes using traditional ovens and stoves. Professional chefs generally find microwave ovens to be of limited usefulness because browning, caramelization, and other flavor-enhancing reactions cannot occur due to the temperature range. A chef is a person who cooks professionally In a professional kitchen setting the term is used only for the one person in charge of everyone else in the kitchen the executive Caramelization or caramelisation is the Oxidation of Sugar, a process used extensively in cooking for the resulting nutty flavor and brown color The Maillard reaction is a Chemical reaction between an Amino acid and a Reducing sugar, usually requiring Heat. [4] On the other hand, people who want fast cooking times can use microwave ovens to prepare food or to reheat stored food (including commercially available pre-cooked frozen dishes) in only a few minutes. Popcorn is one example of a very popular item with microwave oven users. Popcorn or popping corn is a type of corn which explodes from the kernel and puffs up when heated

Variants and accessories

A variant of the conventional microwave is the convection microwave. A convection microwave is a combination of a standard Microwave oven, and a Convection oven. A convection microwave is a combination of a standard microwave and a convection oven. Convection ovens or fan ovens or turbo ovens augment a traditional Oven by circulating heated air using a fan. It allows food to be cooked quickly, yet come out browned or crisped, as from a convection oven. Convection microwaves are more expensive than a conventional microwave and are not considered cost-effective if primarily used just to heat drinks or frozen food. They are usually used for cooking prepared dishes.

More recently, certain manufacturers have added a high power quartz halogen bulb to their convection microwave models while marketing them under names such as "Speedcook", "Advantium" and "Optimawave" to emphasize their ability to cook food rapidly and with the same browning results typically expected of a conventional oven. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in A halogen lamp is an Incandescent lamp in which a Tungsten filament is sealed into a compact transparent envelope filled with an inert gas plus a small amount of Advantium is a line of fast-cooking Electric Ovens for household use sold by General Electric. This is achieved using the high intensity halogen lights at the top of the microwave to deposit large amounts of infrared radiation to the surface of the food. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The food browns while also being heated internally by the microwave radiation and heated through conduction and convection by contact with heated air - produced by the conventional convection portion of the unit. The IR energy which is rapidly delivered to the outer surface of food by the lamps is sufficient to initiate browning and caramelization reactions in a particular food's proteins and carbohydrates, producing a texture and taste much more similar to that typically expected of conventional oven cooking rather than the bland boiled and steamed taste that microwave-only cooking tends to create. Caramelization or caramelisation is the Oxidation of Sugar, a process used extensively in cooking for the resulting nutty flavor and brown color Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most

In order to aid browning, sometimes an accessory browning tray is used, usually composed of glass or porcelain. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. Porcelain is a Ceramic material made by heating raw materials generally including Clay in the form of Kaolin, in a Kiln to temperatures It makes food crisp by oxidising the top layer until it turns brown. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Browning is the process of becoming Brown, especially referring to Food. Ordinary plastic cookware is unsuitable for this purpose since it could melt. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products

Sizes

Consumer microwaves typically come in two types in three sizes:

Increasingly, microwaves are sold with additional features including combining them with convection cooking, "top browning" elements that will brown food (similar to the broiling function on an oven) and even rotisseries in the oven. Most microwaves have white enamel interiors but high end models are often stainless steel, like the original Radarange.

Efficiency

A microwave oven only converts part of its electrical input into microwave energy. A typical consumer microwave oven consumes 1100 W of electricity in producing 700 W of microwave power, an efficiency of 64%. The other 400 W are dissipated as heat, mostly in the magnetron tube. Additional power is used to operate the lamps, AC power transformer, magnetron cooling fan, food turntable motor and the control circuits. This waste heat, along with heat from the food, is exhausted as warm air through cooling vents.

A consideration for rating the efficiency of a microwave oven is to assess how much energy is wasted by using other forms of cooking. So, when heating water for a coffee, say, one heats just the mugful of water. If one uses a kettle, one also heats the kettle itself plus the water plus, usually, extra water which is then left in the kettle. Depending upon the size of the kettle and the amount of excess water, these factors alone can make the 64% quoted above seem very good. Cooking in conventional ovens entails heating the internal structure of the oven to cooking temperature and, additionally, it involves maintaining that temperature against convective and radiative losses of heat for a longer time than is usual with a microwave oven. The efficiencies of conventional cooking methods can be difficult to quantify but they tend to be low.

Safety and controversy

The dominant view has been that microwaved food is as safe to eat as other cooked food. Microwave ovens have become a fairly standard item in most western homes. Microwaving food is fast and energy efficient; however, there are a number of potential safety issues along with decreased safety risks, such as risk of fire.

Benefits and safety features

Commercial microwave ovens all use a timer in their standard operating mode; when the timer runs out, the oven turns itself off.

Microwave ovens heat food without getting hot themselves. Taking a pot off a stove, with the exception of an induction cooktop, leaves a potentially dangerous heating element or trivet that will stay hot for some time. An induction cooker uses Induction heating for Cooking. A conducting pot is placed above an Induction coil for the heating process to take place Likewise, when taking a casserole out of a conventional oven, one's arms are exposed to the very hot walls of the oven. A microwave oven does not pose this problem.

Food and cookware taken out of a microwave oven is rarely much hotter than 100 °C (212 °F). Cookware used in a microwave oven is often much cooler than the food because the microwaves heat the food directly and the cookware is heated by the food. Food and cookware from a conventional oven, on the other hand, are the same temperature as the rest of the oven; a typical cooking temperature is 180 °C (360 °F). That means that conventional stoves and ovens can cause more serious burns.

The lower temperature of cooking (the boiling point of water) is a significant safety benefit compared to baking in the oven or frying, because it eliminates the formation of tars and char, which are carcinogenic. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Microwave radiation also penetrates deeper than direct heat, so that the food is heated by its own internal water content. In contrast, direct heat can fry the surface while the inside is still cold. Pre-heating the food in a microwave oven before putting it into the grill or pan reduces the time needed to heat up the food and reduces the formation of carcinogenic char.

Uneven heating, deliberate and otherwise

In a microwave oven, food may be heated for so short a time that it is cooked unevenly, since heat requires time to diffuse through food, and microwaves only penetrate to a limited depth. Microwave ovens are frequently used for reheating previously cooked food, and bacterial contamination may not be killed if the safe temperature is not reached, resulting in foodborne illness. Leftovers are the uneaten edible remains of a Meal after the diner has finished Eating. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Food safety is a scientific discipline describing handling preparation, and storage of Food in ways that prevent Foodborne illness. Foodborne illness (also foodborne disease) is any Illness resulting from the consumption of food

Uneven heating in microwaved food 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 reflects microwave energy to different parts of the oven as it rotates, or by a turntable or carousel that turns the food; turntables, however, may still leave spots, such as the center of the oven, which receive uneven energy distribution. Reflection is the change in direction of a Wave front at an interface between two different media so that the wave front returns into the medium from which

The second problem is due to food composition and geometry, and must be addressed by the cook by arranging the food so that it absorbs energy evenly, and periodically testing and shielding any parts of the food that overheat. Electromagnetic shielding is the process of limiting the flow of Electromagnetic fields between two locations by separating them with a barrier made of conductive material In some materials with low thermal conductivity, where dielectric constant increases with temperature, microwave heating can cause localized thermal runaway. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. Measurement The relative static permittivity εr can be measured for static Electric fields as follows first the Capacitance of a test Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature leading to a destructive result As an example, uneven heating in frozen foods is a particular problem, since ice absorbs microwave energy to a lesser extent than liquid water, leading to defrosted sections of food warming faster due to more rapid heat deposition there.

Due to this phenomenon, microwave ovens set at too-high power levels may even start to cook the edges of the frozen food, while the inside of the food remains frozen. Another case of uneven heating can be observed in baked goods containing berries. In these items, the berries absorb more energy than the drier surrounding bread and also cannot dissipate the heat due to the low thermal conductivity of the bread. The result is frequently the overheating of the berries relative to the rest of the food. The low power levels which mark the "defrost" oven setting are designed to allow time for heat to be conducted from areas which absorb heat more readily to those which heat more slowly. More even heating will take place by placing food off-center on the turntable tray instead of exactly in the center.

Microwave heating can be deliberately uneven by design. Some microwavable packages (notably pies) may contain ceramic or aluminum-flake containing materials which are designed to absorb microwaves and heat up (thereby converting microwaves to less penetrating infrared) which aids in baking or crust preparation by depositing more energy shallowly in these areas. The word ceramic is derived from the Greek word κεραμικός ( keramikos) Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Such ceramic patches affixed to cardboard are positioned next to the food, and are typically smokey blue or gray in color, usually making them easily identifiable. Microwavable cardboard packaging may also contain overhead ceramic patches which function in the same way. The technical term for such a microwave-absorbing patch, is a susceptor. A susceptor is a material used for its ability to absorb Electromagnetic energy.

Dangers

3. A microwaved DVD-R showing the effects of electrical discharge through its metal film
3. A microwaved DVD-R showing the effects of electrical discharge through its metal film
See also: Microwave-related injury

Liquids, when heated in a microwave oven in a container with a smooth surface, can superheat; that is, reach temperatures that are a few degrees in temperature above their normal boiling point, without actually boiling. DVD-R is a DVD recordable format A DVD-R typically has a storage capacity of 4 Microwave-related injuries are injuries that result from the heating of objects using Microwave radiation. See Superheater for the device used in Steam engines In Physics, superheating (sometimes referred to as boiling retardation The boiling process can start explosively when the liquid is disturbed, such as when the operator takes hold of the container to remove it from the oven or while adding impurities such as powdered creamer or sugar, and can then result in a violent burst of water and vapor resulting in liquid and steam burns. A steam Explosion (also called a Littoral explosion, or fuel-coolant interaction, FCI) is a violent A common myth states that only distilled water can exhibit this behavior; this is not true. Purified water is water from any source that is physically processed to remove impurities [5]

Closed containers and eggs can explode when heated in a microwave oven due to the pressure build-up of steam. An egg is a round or oval body laid by the female of many animals consisting of an Ovum surrounded by layers of Membranes and an outer casing which acts to nourish Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. Products that are heated too long can catch fire. Though this is inherent to any form of cooking, the rapid cooking and unattended nature of microwave oven use results in additional hazard. Microwave oven manuals frequently warn of such hazards, but many of them are difficult to foresee. Because the microwave oven's cavity is enclosed and metal, fires are generally well contained. Simply switching off the oven and allowing the fire to consume available oxygen with the door closed will typically contain damage to the oven itself.

Any metal or conductive object placed into the microwave will act as an antenna to some degree, resulting in an electric current. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant This causes the object to act as a heating element. Joule heating is the process by which the passage of an Electric current through a conductor releases Heat. This effect varies with the object's shape and composition.

Any object containing pointed metal can create an electric arc (cause sparks) when microwaved. An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive This includes cutlery, aluminium foil, ceramics decorated with metal, and most anything containing any type of metal. Cutlery refers to any hand Implement used in preparing serving and especially eating Food in the Western world. WikipediaManual of Style#National varieties of English --> Aluminium foil (known Forks are a good example. This is because the tines of the fork resonate with the microwave radiation and produce high voltage at the tips. Tines or prongs are parallel or branching spikes forming parts of various tools and natural objects Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical This has the effect of exceeding the dielectric breakdown of air, about 3 megavolts per meter (3×106 V/m). The term electrical breakdown has several similar but distinctly different meanings The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The air forms a conductive plasma, which is visible as a spark. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The plasma and the tines may then form a conductive loop, which may be a more effective antenna, resulting in a longer lived spark. Any time dielectric breakdown occurs in air, some ozone and nitrogen oxides are formed, both of which are unhealthy in large quantities. OZONE is an object oriented Operating system written in the C programming language. The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric Microwaving food containing an individual smooth metal object without pointed ends (for example, a spoon) usually does not produce sparking.

The effect can be seen clearly on a CD or DVD (particulalry the factory pressed type). A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is The microwaves induce electric currents in the metal film, which heats up, melting the plastic in the disc and leaving a visible pattern of concentric and radial scars. It can also be illustrated by placing a radiometer inside the cooking chamber, creating plasma inside the vacuum chamber. A radiometer is a device for measuring the radiant flux (power of Electromagnetic radiation.

4. A microwave oven with a metal shelf
4. A microwave oven with a metal shelf

Several microwave fires have been noted where Chinese takeout boxes with a metal handle are microwaved. The Oyster pail, Chinese food box or Chinese takeout container is a folded Paperboard container, traditionally with a Wire Handle Twist ties with an internal metal wire are also notoriously dangerous. A twist tie is a Metal Wire encased in a thin strip of paper or plastic used to tie the openings of Bags such as garbage bags or bread bags

Another hazard is the resonance of the magnetron tube itself. If the microwave is run without an object to absorb the radiation, a standing wave will form. A standing wave, also known as a stationary wave, is a Wave that remains in a constant position The energy is reflected back and forth between the tube and the cooking chamber. This may cause the tube to 'cook' itself and burn out. Thus dehydrated food, or food wrapped in metal which does not arc, is problematic without being an obvious fire hazard. Drying is a method of Food preservation that works by removing Water from the food which prevents the growth of Microorganisms and Decay.

Some magnetrons have ceramic insulators with a bit of beryllium oxide (beryllia) added—these ceramics often appear somewhat pink or purple-colored (see picture#2). The word ceramic is derived from the Greek word κεραμικός ( keramikos) An insulator, also called a Dielectric, is a material that resists the flow of Electric current. Beryllium oxide ( BeO) is a white crystalline oxide It is notable as it is an electrical insulator with a thermal conductivity higher than any other non-metal that actually Note that beryllium oxide is white (see article beryllium oxide), so relying on the color to identify its presence is not reliable. Beryllium oxide ( BeO) is a white crystalline oxide It is notable as it is an electrical insulator with a thermal conductivity higher than any other non-metal that actually The beryllium in such oxides is a serious chemical hazard if crushed and ingested (eg, inhaling dust). Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Single incident or chronic exposure can lead to berylliosis, a serious uncurable condition. Berylliosis or chronic beryllium disease (CBD is an Occupational lung disease. In addition, beryllia is listed as a confirmed human carcinogen by the IARC; therefore, broken ceramic insulators or magnetrons should not be handled. The International Agency for Research on Cancer ( IARC, or CIRC in its French Acronym) is an intergovernmental agency forming part of the World Health This is obviously only a danger if the microwave oven become physically damaged (ie, cracked ceramics) or upon opening and handling the magnetron directly.

Certain foods, if carefully arranged, can also produce arcing, such as grapes. [6] A naked flame, being made of conductive plasma, will do the same, so burning candles, matches, paper, etc should not put in a microwave oven.

Further information: St. Elmo's fire

Controversial hazards

Radiation from a microwave oven directly on a human is not carcinogenic. St Elmo's fire is an electrical Weather Phenomenon in which luminous plasma is created by a Coronal discharge originating from The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation However, with the oven door open, the radiation may cause damage by heating. Nearly every microwave sold has a protective interlock so that it cannot be run when the door is open or improperly latched.

It is unclear whether the effects of microwave radiation on the nutrient contents of food are positive or negative.

Direct radiation

Some people are concerned with being exposed to the microwave oven's radiation. According to the United States Food and Drug Administration's Center for Devices and Radiological Health, a U. S. Federal standard limits microwave leakage from an oven, for the lifetime of the device, to 5 milliwatts per square centimeter when measured 5 centimeters from the surface of the oven. [7] This is far below the exposure level currently considered to be harmful to human health.

The radiation produced by a microwave oven is non-ionizing. Non-ionizing radiation (or esp in British English, non-ionising radiation) refers to any type of Electromagnetic radiation that does not carry enough Therefore it does not have the cancer risks associated with ionizing radiation such as X-rays, ultraviolet light, and high-energy particles. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Long-term rodent studies to assess cancer risk have so far failed to identify any carcinogenicity from 2. 45 GHz microwave radiation even with chronic (ie, large fraction of life span) exposure levels, far larger than humans are likely to encounter from any leaking ovens. [8][9]

When injury from exposure to microwaves occurs, it usually results from dielectric heating induced in the body, the same heating that cooks food. Exposure to microwave radiation can produce cataracts by this mechanism, because the microwave heating denatures proteins in the crystalline lens of the eye (in the same way that heat turns egg white and so opaque) faster than the lens can be cooled by surrounding structures. A cataract is a clouding that develops in the crystalline lens of the Eye or in its envelope varying in degree from slight to complete opacity Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain An egg is a round or oval body laid by the female of many animals consisting of an Ovum surrounded by layers of Membranes and an outer casing which acts to nourish The lens and cornea of the eye are especially vulnerable because they contain no blood vessels that can carry away heat. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body Exposure to heavy doses of microwave radiation (as from an oven that has been tampered with to allow operation even with the door open) can produce heat damage in other tissues as well, up to and including serious burns which may not be immediately evident because of the tendency for microwaves to heat deeper tissues with higher moisture content. A burn is a type of Injury that may be caused by Heat, cold, Electricity, Chemicals, Light, Radiation, or

To put the radiation hazard into perspective, the formation of carcinogenic char in conventional frying pan or oven needs to be taken into account (see above) in a risk comparison. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation The carcinogens in char are toxicated into carcinogens that are radiomimetic (i. Toxication is the process of Metabolism in which the metabolite of a compound is more toxic than the parent drug or Chemical. e. , cause damage similar to ionizing radiation). Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation Microwaving instead of frying or cooking in the oven eliminates this danger.

Effects on food and nutrients

Spinach retains nearly all its folate when cooked in a microwave. [10] In comparison, it loses about 77 percent when cooked on a stove due to the fact that food on a stove is typically boiled, leaching out nutrients. [10] Steamed vegetables tend to maintain more nutrients when cooked on a stovetop than in a microwave. Bacon cooked by microwave has significantly lower levels of carcinogenic nitrosamines than conventionally cooked bacon. Nitrosamines are Chemical compounds of the Chemical structure R1N(-R2-N=O some of which are carcinogenic. [10]

See also

Notes

  1. ^ The History of the Microwave Oven
  2. ^ Raytheon Company: Technology Leadership
  3. ^ Microwave Oven Regression Model
  4. ^ Hervé This, Révélations gastronomiques, Éditions Belin. A TV dinner (also called frozen dinner, microwave meal or ready meal) is a prepackaged frozen or chilled Meal which usually comes in an Microwave chemistry is the science of applying Microwave irradiation to chemical reactions. An induction cooker uses Induction heating for Cooking. A conducting pot is placed above an Induction coil for the heating process to take place A susceptor is a material used for its ability to absorb Electromagnetic energy. ISBN 2-7011-1756-9
  5. ^ Unwise Microwave Oven Experiments
  6. ^ "Why do grapes spark in the microwave?" MadSci Network
  7. ^ US Food and Drug Administration on safety of microwave ovens
  8. ^ PMID 9806599
  9. ^ PMID 9453703
  10. ^ a b c The Claim: Microwave Ovens Kill Nutrients in Food By ANAHAD O’CONNOR. 2006, Cornell University

References

External links

Dictionary

microwave oven

-noun

  1. An appliance for cooking food using microwave energy.
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