a.k.a. Electricity Power

What is electricity?

Electrons in Atoms All matter is made up of atoms. Atoms are comprised of: protons neutrons electrons Electrons circle the space outside the nucleus

How electrons create a charge Electrons carry a negative charge. Electrons can move from one atom to another. The material that picks up an electron is negatively charged. The material that loses an electron is positively charged.

Opposites attract Objects with a net positive charge will be attracted to objects with a negative charge. Two objects with the same charge will repel each other.

Static Electricity Experiment Friction causes electrons to move from one object to another. Rub a balloon against the carpet. The balloon will pick up extra electrons and will be negatively charged. Touch the balloon to the wall. The wall is neutral. What happens?

Experiment with light bulb Experiment with comb and light bulb Can we generate enough of a charge to cause a light bulb to light up?

Electricity in motion Different from static electricity Electrons moving from one atom to the next. Called a current.

Demonstration of current This is a closed circuit.

Demonstration of current The switch allows the circuit to be open and closed.

Lights in series Lights are connected in a continuous circle. If one bulb goes out – the circuit is broken and none work. All bulbs must share the current. The more bulbs on the string, the dimmer the light becomes.

Lights in parallel Each light gets the full amount of current. If one bulb goes out – others will still work. All electricity in home is wired in parallel.

Historical Figures in Electricity

William Gilbert ( ) First person to use the term “electric” Invented a device called the “vensorium” if it moved toward an object then Gilbert called the object electric.

Benjamin Franklin ( ) First to discover the principle of “conservation of charge” - an accounting relationship between the amount of charge in a region and the flow of charge into and out of that region Wanted to verify that lightning was a form of electricity and flew a kite in a storm. The idea was to get lightning to strike the kite and have the charge run down the string to the key attached to the end of it.

Charles Coulomb ( ) Studied the amount of attraction/repulsion between charged objects. Coulomb’s law: the force between two charges is inversely proportional to the square of the distance between them.

Allessandro Volta ( ) Invented the voltaic pile (battery). Volta stacked several pairs of alternating copper and zinc disc separated by cloth. When the top and bottom contacts were connected by a wire, an electric current flowed through the voltaic pile and the connecting wire. The strength of the battery is given in volts.

Georg Ohm ( ) Discovered the concept of resistance. Ohm’s law states that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current. V = I * R

Michael Faraday ( ) Discovered electromagnetic induction which is the the generation of an electric current by passing a metal wire through a magnetic field. Principle behind the operation of generators, transformers, etc…

James Wimshurst ( ) Invented a device (the Wimshurst machine) that could deliver an electric charge. Predecessor to the modern generator – a device that converts mechanical energy to electrical energy.

Thomas Edison ( ) Invented the light bulb Worked on selling the concept of bringing electricity into the home. Edison patented a system for electricity distribution in 1880 (essential for capitalizing on the invention of the electric lamp) and established Edison Illuminating Company providing 110 Volts of DC current to 59 customers in Manhattan. Advocated against AC.

Nikola Tesla (1856 – 1943) Rival of Thomas Edison Developing the modern alternating current (AC) electrical supply system Worked for Edison’s company but left after being treated badly. In 1885, Westinghouse corporation bought the patent rights to Tesla’s system of dynamos, transformer and motors and used Tesla’s alternating current system to light the World’s Columbian Exposition of 1893 in Chicago.

Working with electricity

Measuring Electricity VOLTS (E) measure the “pressure” under which electricity flows. AMPS (I) measure the amount of electric current. WATTS (P) measure the amount of work done by a certain amount of current at a certain pressure or voltage. P = E * I (1 watt = 1 volt * 1 amp)

Measuring Electricity VOLTS (E) measure the “pressure” under which electricity flows. AMPS (I) measure the amount of electric current. WATTS (P) measure the amount of work done by a certain amount of current at a certain pressure or voltage. P = E * I (1 watt = 1 volt * 1 amp)

Measuring Electricity Make some calculations Power (watts) = Voltage (volts) * Current (amps) E.g. A current of 2 Amps flowing through a bulb with 12 Volts across it generates 24 watts of power. Take the quiz: are-Amps-and-Voltshttp://rikravado.hubpages.com/hub/Watt- are-Amps-and-Volts

Power: USA vs. UK USAUK In the USA, the domestic supply is typically 110V (safer than the UK) and this means a 100W bulb draws a current of 100/110 Amps (about 0.9A). In the UK, domestic power is supplied at 240 Volts. A 100 Watt bulb will therefore draw a current of 100/240 Amps (about 0.4A).

What do fuses do? A fuse is used in a circuit to protect the other elements in a circuit. Fuses are rated at different currents and voltages. When the rated current is exceeded the fuse will blow. For example you find fuses in your home. If there was a sudden surge in current coming into your house the fuse will blow and power will be cut to the circuit it is attached to. If that fuse wasn't there the other elements in that circuit would be exposed to the current surge. This would cause damage to that object Patented by Thomas Edison.

Conductors vs. insulators A good conductor is a material where each atom has one or more free electrons. These become mobile free electrons that create a charge. Good Conductors Copper Silver Graphite Charcoal Watery Materials Good Insulators Wood Fibrous materials Chalk Hair Feathers Dried Vegetables

What is resistance? Not all conductors are equal Some metals allow electrons to move more freely than others – we call them less resistant than others. Copper has low resistance, silver is slightly higher. The longer the wire – the more the resistance. The discovery of resistance was quantified by Georg Ohm who stated: V = I * R – where R is resistance

What are resistors? Resistors are included in a circuit to add resistance. Using Ohm’s law, you can figure out what type of resistance to use to achieve a certain current with a given amount of voltage. Practice making calculations: om/calculator-ohm.htm om/calculator-ohm.htm

How to we manufacture and manage electricity?

What is AC (alternating current)? Power supplied to homes and buildings is AC current. Alternating Current (AC) flows one way, then the other way, continually reversing direction. An AC voltage is continually changing between positive (+) and negative (-).The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards- backwards cycles per second.

Advantages of AC current Travels farther without losing energy and can transfer different amounts of power. AC voltage from a generator in a power plant can be bumped up or down in strength by another mechanism, called a transformer.

How do you make AC? If a machine is constructed to rotate a magnetic field around a set of stationary wire coils with the turning of a shaft, AC voltage will be produced across the wire coils as that shaft is rotated, in accordance with Faraday's Law of electromagnetic induction. This is the basic operating principle of an AC generator, also known as an alternator:

How do AC appliances work? AC appliances don’t care that the electrons are not moving continually in one directions – just that electrons are moving at all.

How is electricity generated at a power plant? Some fuel source, such as coal, oil, natural gas, or nuclear energy produces heat. The heat is used to boil water to create steam. The steam under high pressure is used to spin a turbine. The spinning turbine interacts with a system of magnets to produce electricity. The electricity is transmitted as moving electrons through a series of wires to homes and business.

What is a transformer? Transformers are used wherever an electrical voltage needs to be increased or decreased. They are commonly seen on electrical poles. Power plants produce electricity at a very high voltage so that it can travel great distances. The voltage must be reduced, however, before the electricity reaches homes and other buildings that use it to power appliances, machinery and other devices.

How does electricity get to your home? Electricity is made at a power plant by huge generators. Most power plants use coal, but some use natural gas, water or even wind. The current is sent through transformers to increase the voltage to push the power long distances. The electrical charge goes through high-voltage transmission lines that stretch across the country. It reaches a substation, where the voltage is lowered so it can be sent on smaller power line

How does electricity get to your home? It travels through distribution lines to your neighborhood, where smaller pole-top transformers reduce the voltage again to take the power safe to use in our homes. It connects to your house through the service drop and passes through a meter that measures how much our family uses. The electricity goes to the service panel in your basement or garage, where breakers or fuses protect the wires inside your house from being overloaded. The electricity travels through wires inside the walls to the outlets and switches all over your house.

Discussion / Research

Questions to investigate Where is most of the electricity generated for the St. Louis population? How much electricity does the typical American use? How does electricity usage in the US differ from usage in other countries? Is it possible to convert AC to DC power or vice versa? Where is DC power used? Why is it appropriate in these settings?