Microwave

Global Electricity Consumption

Electricity in Thailand

Let’s get started:

what is electricity? 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

History of electricity 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 toHans Christian Ørsted & André-Marie Ampère

(1819-1820Michael Faraday invented the electric motor

(1821)Georg Ohm mathematically analyzed electrical

circuit (1827)Hans Christian Ørsted André-Marie Ampère Benjamin Franklin Georg Simon Ohm Michael Faraday

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.

How electricity is generated??

We all enjoy the benefits of electricity…. 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.

Inventor of the microwave oven Percy Lebaron Spencer

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 of5.4 x10 amps at 120 volts AC.

To convert power to current, use the equation …

P = VI

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.

EM Wave

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.

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.

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.

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.

References http://www.northwesternenergy.com/

documents/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=.iopscience

http://en.wikipedia.org/wiki/Electricity http://www.ehow.com/how-does 4564448

microwave-magnetrons-work.html

GROUP 3

Chitlada

Ekachai

Nattapol

Nopparat

Suchanuch