how do microwave ovens work physics

Microwave ovens use electromagnetic waves at a frequency of 2.45 GHz (wavelength about 12 cm)that make water molecules vibrate fast and heat up. Unlike conventional stoves, microwave ovens do not have heating elements. This imposes certain limitations on the types of foods that can be heated. The ventilation system may lead to an exterior vent, or it may simply recirculate air back into the kitchen. One thing you might have noticed is that the 2.4GHz frequency of the microwaves used in microwave ovens sounds familiar. When the microwave photons interact with food, food molecules are physically agitated, transforming the EM energy into kinetic energy, or energy of movement. This process is illustrated in Figure 2. So, to the microwaves, this grid of wires looks like a solid wall, and most of it keeps bouncing around inside the oven until it hits an excitable water molecule. (Black arrows represent electric field. Another important application of microwaves is radar. In the first (but by no means the last) microwave cooking accident, the egg exploded, showering an inquisitive colleague with egg and boiling water. Figure 3: Movement of microwaves within a microwave oven (Riaz 2007). IEEE Spectrum, September 30, 2016. Advantages are: A microwave oven designed to be mounted over a cooktop is usually equipped with a ventilation system to cope with the cooking odors, smoke and moisture that rise from the cooking surface. Rotating turntables are included in most microwave ovens and move the food around in attempt to spread the effect of the heating “hotspots” over all of the food; the effect of constructive and destructive interference is not localized to particular points in the food (Heckert 2007). It is common belief that heating any kind of metal inside a microwave oven can be hazardous (‘Today’s Microwaves Can Handle Metal Objects’ 2007). How do microwaves heat up your coffee? The principle of heating food in a microwave oven is based on a molecule’s ability to rotate. Microwave ovens use electromagnetic waves at a frequency of 2.45 GHz (wavelength about 12 cm) that make water molecules vibrate fast and heat up. Either way, don't mess with big voltages. ), The Production of Microwaves in a Magnetron, Limitations & Consequences of Using Microwave Heating, http://www.gallawa.com/microtech/magnetron.html, http://physics.suite101.com/article.cfm/how_do_microwave_ovens_work, http://physics.suite101.com/article.cfm/microwave_ovens_heat_food_unevenly, http://physics.suite101.com/article.cfm/why_no_metal_in_microwave_ovens, http://www.cabrillo.edu/~jmccullough/Applets/Applets_by_Topic/Superposition_Interference.html, http://hyperphysics.phy-astr.gsu.edu/hbase/waves/magnetron.html, http://www.madehow.com/Volume-1/Microwave-Oven.html, http://www.chemistryquestion.com/English/Questions/ChemistryInDailyLife/23c_microwave_metal.html. But how does a microwave work? This excitement means it moves faster, and the water heats up. How magnetrons in microwaves have caused problems for astronomers. This can be problematic as when the microwaves are not absorbed, they accumulate and may eventually reflect back into the magnetron, which can potentially damage it (Chemistryquestion.com 2003). See this in action! Inside your microwave oven, electrical energy is transformed into EM energy in the magnetron. Microwaves do not use x-rays or gamma rays, and they do not make food radioactive. How does a microwave oven heat without heat? Microwaves tend to reflect off of metals, which is useful for the purposes of keeping microwaves from escaping the oven chamber. ALL RIGHTS RESERVED. Since microwaves have a wavelength of about 12.2 cm, the distances between these two extremes is usually only a few centimeters—this can be problematic with respect to heating food (Heckert 2007). Like this! Microwaves sent through the atmosphere will be absorbed by water so they can be used to monitor rain. Thomlet, J 2000, ‘Microwave; Anatomy How it works’, Sydney Morning Herald 02 March, p. 38, viewed 7 August 2010, eLibrary. Heckert, P 2007, Microwave Ovens Heat Food Unevenly, Suite101, viewed 31 August 2010, . Many older plates and other dishes may contain some water or other materials that absorb microwaves, which means you'll end up heating the dish and not the food. Likewise, with all the tricks you see on YouTube about putting CDs or metal objects in microwaves. - paper So noise (if not too big) can be overcome. A Brief History of the Microwave Oven by Evan Ackerman. However, if metal is used as a container for the food being heated, the microwaves will be reflected rather than absorbed by the food; the food stays cold. Your Wi-Fi devices use the same frequency, but at much lower power: while a typical microwave oven can generate several hundred watts of microwave radiation, your Wi-Fi devices are emitting only a few milliwatts of radiation. Some ovens also feature a rotating metal fan (called the stirrer) which spreads the microwave beam to make it more random. The microwaves are reflected within the metal interior of the oven where they are absorbed by food. The radiation is kept inside the oven by the reflecting metal case and metal grid in the door. The device was patented in 1945 by Spencer for the Raytheon Corporation. They are also used for supervisory control and data acquisition (SCADA) for remote machinery, switches, valves and signals. Microwave ovens work by using very high levels of a certain frequency of RF radiation (in the microwave spectrum) to heat foods. Microwaves are created by the Magnetron, are sent in different directions by the stirrer, bounce off metal surfaces, and are absorbed by the water in food. Thus, ice is not heated as effectively by microwaves, and must be heated by means of normal heat conduction (Heckert 2007). Conduction and convection processes spread the heat through the food. Watch water molecules rotating and bouncing around. Once the microwaves are inside the cooking cavity, they bounce around until they hit something that can absorb them, such as a water molecule. Microwaves are an essential part of the modern kitchen due to their ability to quickly and easily heat food and drink. Microwave heating remains the most efficient way to reheat food, and there is nothing on the horizon at present that looks likely to challenge that. Microwaves are produced inside the oven by an electron tube called a magnetron. CNET también está disponible en español. Later during 1888 Heinrich Hertz (third picture) proved the existence of microwaves by building a device that produced and detected microwave … Microwave transmissions Wireless technology uses microwaves and radio waves to transmit information. Additionally, because microwaves consist of an electric field, the mobilized electrons in a metal’s surface move according to the oscillations of the electric field. Because it uses less energy and is much quicker than a gas or electric ovens, the microwave has found a spot in most homes. This structure is shown in Figure 1. What has happened is that microwave ovens have got cheaper and cheaper, thanks to the increasing efficiency of manufacturing. Constructive and destructive interference between microwaves can cause uneven heating in the food. The resulting paths some electrons might take are shown in Figure 1. "But wait!" Heat between a source and a recipient can be transferred in three ways: conduction, when the two are in direct contact, like when you touch a hot cup; convection, when the heat is transferred by a medium, usually fluid, like when hot air contacts colder air; and finally, radiation, when the heat is transferred by the means of an electromagnetic wave, which requires no medium to propagate, such as the warmth imparted by the sun’s ligh… Microwaves could affect your tissue in a similar way if they were able to escape from the microwave oven. The weaker the signal reaching the detector, the more rain the microwaves have passed through. Year 12 Physics Information Search Presentation. There must always be something to absorb the microwave… Of course, you don't want things outside the oven getting heated up, which is why they are made of metal. In a thick metal object, the heat created from this friction can dissipate, but a thin object will become very hot very quickly (Chemistryquestion.com 2003). Metallic objects with sharp points (such as forks) can have strong electric charge build up on their tips, causing air particles to be ionized, and thus allowing the excess charge to jump to the nearest conductor, creating sparking (Heckert 2007). A permanent magnetic field exists perpendicular to the electric field and parallel to the length of the tube. Adjust the frequency and amplitude of microwaves. (Interactive Java applet from PhET.). This is why microwaves are so good at re-heating food: rather than heating the food from the outside like a normal oven would, they heat the water within the food, so it heats up quicker and more evenly. When the microwaves go through the food, they make the water molecules vibrate. Intrigued, he used this device to cook popcorn and an egg. They produce microwave beams whose spreading angle is proportional to the ratio of the wavelength of the constituent waves to the diameter of the dish. Figure 4: The rotation of water molecules under the influence of the electric field component in an electromagnetic wave. They accelerate towards the anode, the outside of the tube, due to the force applied on them by the electric field. A mobile phone receives microwave signals from a nearby phone mast (or ‘transmitter’) and sends microwave signals back. If the interference is destructive, there may be no resulting electric field so the food will stay cold at that point (Heckert 2007). Why is it prohibited to warm up metal by microwave? It is one of the odd quirks of radiation that if a hole is smaller than the wavelength of the radiation, most of it won't pass through the hole. The behaviour of an electromagnetic wave in a substance depends on its frequency. How do mobile phones work? The secret of the microwave is in, well, the microwaves. Microwaves sent through the atmosphere will be absorbed by water so they can be used to monitor rain. If you look closely, you'll see a grid of wires inside the clear glass door. Ever since humans first dropped a chunk of mammoth meat onto a fire and liked the result, we have been looking for new ways to cook things. The microwave oven had its origins in radar research before and during World War II. The frozen burrito in your microwave oven sits in an electromagnetic field, bombarded on all sides by high-frequency microwaves. The frequency at which this resonation occurs is consistent with that of microwaves; since electric and magnetic fields are emitted perpendicularly to each other and perpendicular to the direction of travel at this frequency, microwaves are effectively emitted. But just to say it again, DON'T TRY THIS AT HOME, JUST WATCH IT ON YOUTUBE. This device takes the form of a hollow tube, with a cylindircal cathode running through the centre and the outside of the tube, shaped with several cavities, acting as an anode (Gallawa 2008). Thus, in the presence of the electric field component of a microwave, a force will be applied to both dipoles of the molecule which will cause it to rotate (Heckert 2007). Microwaves are widely used for heating in industrial processes. This is also the reason why microwaves are built so they won't work when the door is open, and why messing with this is a VERY BAD IDEA. That's pretty good progress for a device that was invented by accident 55 years ago. Let's zap some lunch and find out. In fact, it is thought that that by the beginning of the 21st century, over 90 percent of homes in the US had a microwave oven. And hot water in your food means, as the heat spreads, hot food. Microwave ovens work by using 2.45 GHz frequency electromagnetic waves know as microwaves to heat the water in food. Advantages are: It does explain, though, why your Wi-Fi devices sometimes stop working when someone makes popcorn; although most of the microwave radiation is contained by the oven, a small amount escapes and can overwhelm the Wi-Fi signal. Modern microwave ovens are designed to allow essentially no leakage of microwaves, however. n a microwave oven, special antennas radiate electromagnetic waves. However, modern magnetrons are built to handle large amounts of microwave input, so usually this microwave reflection is relatively harmless (‘Today’s Microwaves Can Handle Metal Objects’ 2007). Microwaves were first predicted by James Clerk Maxwell (second picture) in 1864 by use of his equations. If the food doesn't have any water in it, it won't absorb microwaves and it won't heat up. In a microwave oven, microwaves are produced by a device called a magnetron. How Raytheon's Percy Spencer pioneered a new way of cooking—with waves. One of the more recent developments in this race to taste is the microwave oven, which uses microwave radiation to heat and cook your food. How does a microwave oven heat without heat? By the Kinetic Particle Theory, if the particles in the food have more kinetic energy, then the food will be hotter. Thus, an electric field exists in the gap inside the tube. Microwaves are absorbed by some of the chemicals in foods—most optimally water. This current has got to go somewhere, and the easiest path between bits of metal is sometimes through the air (such as between the tines of a fork). "What about the door? Because of their curved motion, the electrons are pushed towards an area where there is excess negative charge in the anode (one side of a cavity.) Cooking metal objects in a microwave is ANOTHER VERY BAD IDEA because the microwave can induce an electric current in metal. In a microwave oven, microwaves are produced by a device called a magnetron. This magnetic field forces these electrons to circle around inside the cavity, absorbing energy. Microwave oven radiation will heat up our body cells and is very dangerous at high intensity because it will burn body tissue. Microwave ovens cook foods by injecting them with, surprise, microwaves —a form of energy. While walking past a magnetron being tested, an eccentric engineer called Percy Spencer noticed that the radiation melted his candy bar. Created in a device called the magnetron, these electromagnetic waves get water excited. Thus, the water molecules are rotating as quickly as possible. The wavelength (distance from one field wiggle to the nect) is much longer for microwaves than for light. For example, ice is a solid and so its molecules cannot rotate as easily as in liquid water. Figure 1: Electrons emitted from the cathode undergo curved motion towards the anode (Nave 2005). Radio waves, microwaves, infrared and visible light. A microwave oven passes microwave radiation at a frequency near 2.45 GHz (12 cm) through food, causing dielectric heating primarily by absorption of the energy in water. However, this phenomenon too is mostly harmless to the food and the microwave oven (‘Today’s Microwaves Can Handle Metal Objects’ 2007). Riaz, R 2007, How Products are Made: Microwave Oven, Advameg, viewed 7 August 2010, . Electromagnetic wave's forces act on charges, pushing positive charges (+) one way and … It's the same reason why broadcast TV antennas made of grids of wire work: the grid looks like a solid surface to the radiation. At every point in the oven chamber, there are several microwaves interfering with each other, meaning the resulting electric field at that point is the sum of their respective electric fields. The microwaves penetrate about 1 cm into the food. Figure 2: Electrons cause excess negative charge to be pushed back around the cavity, creating microwave oscillations (Nave 2005). For food to be heated in a microwave oven, microwaves must pass through the food. A microwave oven is basically a metal box containing a magnetron. The microwaves produced by the magnetron are directed towards a spinning propellor made of metal. The typical size of these waves is a few centimeters. As my physics teacher used to say, "It's the volts that jolts, and the mills that kills", because a high voltage won't kill you, but a small amperage (in the milliamp range) across the heart for a couple of seconds is enough to stop your heart beating and kill you. The weaker the signal reaching the detector, the more rain the microwaves have passed through. So, microwave ovens are likely to remain a mainstay of the modern kitchen for many years to come. Objects containing minimal water will also take longer to be heated, as there will be less water molecules rotating and thus less kinetic energy being transferred to the food. Microwaves are used mostly for point-to-point communications systems to convey all types of information, including voice, data and video in both analog and digital formats, according to the Federal Communications Commission (FCC). These are connected to the metal walls of the oven, and block the microwaves from getting out. Microwave ovens. 2003, Chemistryquestion.com, viewed 7 August 2010, . Microwave Ovens Posing as Astronomical Objects by Alexander Hellemans. It is not only ovens that make use of microwaves – they are also used to send information from your mobile phone, whether it is a conversation, a text message, a photograph or even a video clip. Nave, R 2005, The Magnetron, viewed 31 August 2010, . When food absorbs microwaves, it causes the water molecules in the food to vibrate, which produces heat. Gallawa, J 2008, The Magnetron Tube Used In Microwave Ovens, viewed 31 August 2010, . Does that mean every time I look through this my eyeballs are being boiled?". This excess negative charge is pushed back around the cavity, creating an oscillation of electric and magnetic fields due to a moving charge (Nave 2005). The interaction of these molecules undergoing forced rotation creates heat, and the food is cooked. Like waves in a bathtub, this reflection produces peaks (with lots of microwaves) and troughs with few microwaves, which scientists call a standing wave. The frequency of microwaves (2.45 GHz) is optimal because the time it takes for the electric field to oscillate is consistent with the time it takes for a water molecule to rotate 180° (Heckert 2007). This process of generating microwaves requires a very high voltage, usually in excess of a thousand volts (1 kilovolt). This is also why you need to be careful about both the food and the dishes you use in a microwave. - … CNET … Newer Wi-Fi devices that use the 802.11ac standards don't have this problem, as they send and receive data at a higher frequency of 5GHz. The word \"radar\" was originally an acronym for RAdio Detection And Ranging. Microwaves work by shooting waves called microwaves through food. Microwaves have wavelengths approximately in … Microwave transmitters and receivers are parabolic dish antennas. So how do microwaves work then? IEEE Spectrum, May 5, 2015. Microwave cookers use waves which give energy to the water molecules in food, causing the food to get hot. Microwave ovens work by using microwave about 12 centimeters in length to force water and fat molecules in food to rotate. Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) wavelengths, but relatively short for radio waves. As the name suggests these devices use microwave radiation, with a frequency of about 2.4GHz and a wavelength of about 4 inches (10.16 cm). How does a microwave turn electricity into heat? Undeterred, Spencer attached the magnetron to a metal box, and the first microwave oven was born. Water absorbs the energy from the electromagnetic waves and turns that energy into thermal motions causing the temperature of the food to increase. Microwave transmissions Wireless technology uses microwaves and radio waves to transmit information. These electromagnetic waves are invisible to the human eye and fall between radio waves, which are longer in wavelength, and infrared waves, which are shorter. The beams can thus be directed like a searchlight. The same is true of cracked or damaged dishes, where water can get into the crack and expand rapidly as it is heated, breaking the dish. This creates a plasma of ionized gas which can start a fire. Fortunately, the answer is no. Working of microwave oven A microwave oven, commonly referred to as a microwave, is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation in the microwave spectrum. How Raytheon 's Percy Spencer pioneered a new way of cooking—with waves of his equations vacuum cavity! 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And the dishes you use in a microwave exists in the food to increase that! Surrounding them and how do microwave ovens work physics some of the physical concepts involved in their operation to... Thus be directed like a searchlight, where the microwaves from getting out cheaper, thanks the., bombarded on all sides by high-frequency microwaves molecules in the food rotate. Heated in a microwave oven is basically a metal box containing a magnetron are a lot like waves.

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