student presentation theme: electricity in daily life muic mahidol 2009

4.  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

5.  June, 1752, BenjaminFranklin 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
 HansChristianØrsted& André-Marie Ampère(1819-1820
 MichaelFaradayinvented the electric motor (1821)
 GeorgOhm mathematically analyzed electrical circuit (1827)
Hans Christian Ørsted André-Marie Ampère Benjamin Franklin Georg Simon Ohm Michael Faraday

6. 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.

7. How electricity is generated??

8.  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 presentationwe are goingtomainly focus
onmicrowaveswhichis one of themain
electronicdevices inour dailybasis.

9.  Percy Lebaron Spencer

10. 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 …

11. 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

12. EM Wave

13. 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.

14. 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.

15. 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.

16. 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.

17. References
 http://www.northwesternenergy.com/doc
uments/E+Programs/E+Green.pdf
 http://www.eia.doe.gov/kids/energyfacts/
sources/electricity.html
 http://iopscience.iop.org/0031-
9120/39/1/006/pdf?ejredirect=.iopscienc
e
 http://en.wikipedia.org/wiki/Electricity
 http://www.ehow.com/how-does
4564448 microwave-magnetrons-
work.html