Introduction

Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms, and an atom has a center, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons. When the balancing force between protons and electrons is upset by an outside force, an atom may gain or lose an electron. When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current. 

Electricity is a basic part of nature and it is one of our most widely used forms of energy.  We get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. Before electricity generation began slightly over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite one stormy night in Philadelphia, the principles of electricity gradually became understood. In the mid-1800s, Thomas Edison changed everyone's life -- he perfected his invention -- the electric light bulb. Prior to 1879, electricity had been used in arc lights for outdoor lighting. Edison's invention used electricity to bring indoor lighting to our homes.

How is a transformer used?

To solve the problem of sending electricity over long distances, George Westinghouse developed a device called a transformer. The transformer allowed electricity to be efficiently transmitted over long distances. This made it possible to supply electricity to homes and businesses located far from the electric generating plant. 

Despite its great importance in our daily lives, most of us rarely stop to think what life would be like without electricity. Yet like air and water, we tend to take electricity for granted. Everyday, we use electricity to do many functions for us -- from lighting and heating/cooling our homes, to being the power source for televisions and computers.  Electricity is a controllable and convenient form of energy used in the applications of heat, light and power. 

How is electricity generated?

An electric generator is a device for converting mechanical energy into electrical energy.  The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire. The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. Each section of wire constitutes a small, separate electric conductor. All the small currents of individual sections add up to one current of considerable size. This current is what is used for electric power.

An electric utility power station uses either a turbine, engine, water wheel, or other similar machine to drive an electric generator or a device that converts mechanical or chemical energy to electricity. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity. 

A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. Steam turbines have a series of blades mounted on a shaft against which steam is forced, thus rotating the shaft connected to the generator. In a fossil-fueled steam turbine, the fuel is burned in a furnace to heat water in a boiler to produce steam.

The electricity produced by a generator travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the electricity to a substation. Substations have transformers that change the high voltage electricity into lower voltage electricity. From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.

How is electricity measured?

Electricity is measured in units of power called watts. It was named to honor James Watt, the inventor of the steam engine. One watt is a very small amount of power. It would require nearly 750 watts to equal one horsepower. A kilowatt represents 1,000 watts. A kilowatt-hour (kWh) is equal to the energy of 1,000 watts working for one hour. The amount of electricity a power plant generates or a customer uses over a period of time is measured in kilowatthours (kWh). Kilowatthours are determined by multiplying the number of kW's required by the number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have used 200 watts of power, or .2 kilowatthours of electrical energy.

Conductors and Insulators

Most materials fall into two groups:

• Conductors - allow electrons, and therefore a current, to flow through them.
• Insulators - do not conduct electricity

There is a small third group called semi-conductors. These partially conduct electricity but have different properties to conductors. For example, as they are heated, their resistance goes down. Conductors' resistance increase as they get hotter.

Current is carried by electrons. Metals contain a "sea" of free electrons (negatively charged) which flow through the metal. This is what allows electric current to flow so well in all metals.

Some important facts that you really should know:

• Conventional current flows from Positive to Negative
• Electrical current flows from Negative to Positive
• So electrons flow opposite to the flow of conventional current

Types of Circuits

Series Circuits

• Components are connected from end to end
• Total resistance is the product of all the resistances added together
• If one component is removed or disconnected the circuit is broken
• Same current in all parts of the circuit
• Total voltage of the supply is shared between components
• The bigger the resistance of a component, the bigger its share of voltage

• Each component separately connected
• If one of the components is disconnected then it does not effect those it is parallel with.
• All components get the full source voltage (therefore the voltage is the same in all the components)
• The lower the resistance of a component the greater the current
• Total current in the circuit is equal to the sum of the currents in its separate branches
• Total current going into a junction is equal to the total current leaving it

 source: http://www.eia.doe.gov/kids/