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Intro to Electricity What is electricity? How is it created? How is it transmitted?

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Electricity Electricity is a form of energy Generally defined as the flow of electric charge from one place to another This is not entirely accurate, but the metaphor works Two sub-atomic particles Protons Positive charge. Large relative mass Electrons Negative charge. Very little relative mass

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Electricity Electric power is created by detaching electrons from an atom This leaves behind a net positive charge This positive charge pulls electrons from neighboring atoms and a “flow” begins Not all atoms easily allow their electrons to break free Good conductors – easily freed electrons Copper, aluminum, gold, platinum Insulators – electrons are VERY hard to break free Most plastics, silicone rubber, porcelain, glass

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Alternating current Voltage will change with time In most instances, it happens very fast 50 cycles per second (Hz) Europe and most of Asia 60 cycles per second (Hz) United States, some of Asia and some South America

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Alternating current James Clerk Maxwell Discovered that electricity and magnetism are two forms of the same physical phenomenon. Maxwell’s laws “A changing magnetic field will produce an electric field” “A changing electric field will produce a magnetic field” How a generator works 3 massive coils of wire which are caused to spin around a permanent magnet. Coils are moving through a magnetic field and this causes electrons to begin moving While moving from north to south, electrons flow one way. From south to north they move the other way Causes three phase electricity. The number of times per sec that the coil revolves will determine the frequency of the electric current Induced current As the voltage rises and falls in an AC circuit, there will be a varying magnetic field produced around the conductor. This magnetic field will in turn produce an electric current in any conductors which are nearby Lighting cable, motor cable, sound power feeds, building air conditioning power… Induces noise in sound lines

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Direct current Often the product of a chemical reaction Batteries Can be generated using an alternator Can be converted from AC current Voltage stays constant over time.

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Ohms Law Voltage, current and resistance are all related Voltage – Also called Electromotive Force (EMF) The potential charge between two points It is a relative measurement We usually measure voltage with respect to “ground” or “earth” Requires a complete path back to ground in order to “flow” Current The “flow” of electrical charge carriers

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Current Flow Water analogy Wire = hose Voltage = water pressure Current = flow of water Resistance = resistance to water flow Kink in the hose A larger hose connected to a smaller hose

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Ohms Law V=IR P=VI V= voltage (volts) I = current (amps) R = resistance (ohms) P = power (watts) VIRP

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Ohms Law These two formulas allow us to relate voltage, current resistance and power to each other. If you know any 2, you can now the other 2. Strictly speaking this is only for DC circuits For AC circuits, resistance is replaced with impedance Takes into account capacitors and inductors

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Circuits Series Electricity flows through each component R T =R 1 +R 2 +R 3 …

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Circuits Parallel The current breaks up, with some flowing along each parallel branch and re-combining when the branches meet again.

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