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

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 presentation we are going to mainly focus
on microwaves which is one of the main electronic
devices in our daily basis.

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 operate at
frequencies of about 2.45 GHz, i.e. λ = 12.23 cm.

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/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