Microwave (student preso)

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general physics 1
presentation 3 group 3
electricity in our daily lives
7 mar 2009

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Microwave (student preso)

  1. 1. Electricity is a general term for phenomena resulting from the presence and flow of electric charge such as lightning, static electricity, electromagnetic field and electromagnetic induction. Electric Current - movement of electric charge is usually measured in amperes and consists of any moving charged particles
  2. 2. June, 1752, Benjamin Franklin attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky. A succession of sparks jumping from the key to the back of his hand show electrical lightning in nature. In electromagnetism, is due to Hans Christian Ørsted & André-Marie Ampère (1819-1820 André- Michael Faraday invented the electric motor (1821) Georg Ohm mathematically analyzed electrical circuit (1827) André-Marie Ampère Georg Simon Ohm Michael Faraday Benjamin Franklin Hans Christian Ørsted
  3. 3. How electricity is generated?? Electricity generation - process of converting non- electrical energy to electricity - mostly generated at a power station by electromechanical generators. Electricity has been generated at central stations since 1881. The first power plants were run on water power or coal Today we rely mainly on coal, nuclear, natural gas, hydroelectric, and petroleum.
  4. 4. How electricity is generated??
  5. 5. Lighting our homes and offices. Keeping the food in our refrigerator cold. Enable us to used many electronic devices such as computers, printers and also MICROWAVES…. In our presentation we are going to mainly focus on microwaves which is one of the main electronic devices in our daily basis.
  6. 6. Percy Lebaron Spencer
  7. 7. What is Microwave (Microwave oven)? A microwave oven is an appliance using electromagnetic energy to heat and cook foods. A microwave oven uses microwaves. Microwaves are very short radio waves commonly employed in radar and satellite communications. Microwave ovens consume power at a rate of 650 - 1200 watts, which corresponds to a current of 5.4 x10 amps at 120 volts AC. To convert power to current, use the equation …
  8. 8. What is Microwave? Microwaves - a form of electromagnetic waves Electromagnetic waves - wavelike oscillations of electric & magnetic fields. These fields are perpendicular to each other and continually oscillate between maximum positive and maximum negative. Their frequencies (wavelengths) are in the range from 300 MHz (λ = 1 m) up to 300 GHz (λ = 1 mm). Following international conventions, microwave ovens at home or in restaurants operate at frequencies of about 2.45 GHz, i.e. λ = 12.23 cm.
  9. 9. EM Wave
  10. 10. How Do Microwaves Heat Food? Microwave heating works by heating the water in foods. The frequency used in microwave ovens optimally heats water molecules. The microwave energy is converted into heat energy of the water molecules, which in turn heat the other molecules in the food. That is why dry foods such as rice and pasta will not cook in a microwave unless they are in some water. The process is like frictional heating. Microwave energy converts to heat energy by causing the molecules in food to increase the speed of their random motions.
  11. 11. Generation of microwaves in magnetrons Most microwave ovens use magnetrons. First invented in 1921 and strongly improved around 1940, magnetrons allow either continuous or pulsed microwave generation with powers up to megawatts and frequencies between 1 and 40 GHz. Efficiencies are around 80% and lifetimes about 5000 hours.
  12. 12. How the Magnetron Works?? The process begins when an electrical current is sent to the cathode/filament. The heat that results from the electrical current causes an increase in molecular activity, thereby emitting electrons into the space between the cathode and anode. This results in the electrons moving away from the cathode and toward the anode, at higher rates of speed as the temperature rises and causes more molecular activity.
  13. 13. How the Magnetron Works?? The electrons follow the antenna toward the anode. During this process, the electrons encounter the magnetic field, which detracts the electrons from their destination. The forces of the electric charge, together with the magnetic field, cause the electrons to travel in an ever- expanding circular orbit until the electron finally reaches the anode. This circular motion of electrons is what produces the microwaves of energy that allows food to be rapidly heated within the contained space of the microwave oven.
  14. 14. References http://www.northwesternenergy.com/docum ents/E+Programs/E+Green.pdf http://www.eia.doe.gov/kids/energyfacts/so urces/electricity.html http://iopscience.iop.org/0031- 9120/39/1/006/pdf?ejredirect=.iopscience http://en.wikipedia.org/wiki/Electricity http://www.ehow.com/how-does 4564448 microwave-magnetrons-work.html

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