Electricity

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Electricity
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Electric Charge and Polarity

• Electric Charge Rules
• More protons than electrons charge
• More electrons than protons - charge
• Like charges repel opposite charges attract
• In electricity, ONLY e- move, not protons!
• Strength of electric force due to amount of
  excess or charge
• Electric Field region around charged particles
  in which others will attract or repel

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Static Electricity

• Definition the buildup of charge on an object
• Method of Charging
• Friction-movement of electrons from one objects
  surface to another
• Conduction-transferring electrons from one object
  to another by direct contact
• Ex. Many metals allow electrons to flow

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Static Electricity cont.,

• Voltage-
• Energy or push that makes electrons move
• The h the voltage, the h energy each electrons
  carries
• Measured in units called volts (V)

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Flow of Electricity

• Electric Current flow of e- through a wire
• Symbol for current is I
• Current is measured in amperes, or amps (A) for
  short
• h current h e-

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Flow of Electricity cont.,

• Resistance opposition to flow of electricity
• Symbol for resistance is R
• Resistance is measure in ohms, which is
  represented by O
• Poor conductors have high resistance (or low
  conductivity)
• Ex. Iron
• Good conductors have low resistance (or high
  conductivity)
• Ex. Copper
• Long and thin wires have more resistance than
  short and thick wires
• Any device that you plug in is called a resistor
  (load)

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Flow of Electricity cont.,

• Ohms Law
• current in a wire voltage/resistance (IV/R)
• See Ex. Problems on pg. O
• 453
• Current Directions
• Direct Current (DC) electrons flow in the same
  direction
• Ex. Batteries (e- flow through and terminal)
• Alternating Current (AC) Electrons constantly
  change their direction of flow
• Ex. Electricity from power plants (via
  generators)

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Electric Currents

• Whats a Circuit?
• Provides a complete, closed path for an electric
  current to flow
• Circuit works when path is closed doesnt work
  when path is open
• Parts of a Circuit
• A source of e- (i.e. battery, outlet)
• A load (resistance) which is the device that uses
  the electricity
• Wires carry the electrons
• A switch, which opens or closes the circuit

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Series Circuit

• Only one path for a current to flow
• All parts of the circuit are connected to one
  after the other
• Ex. Old Christmas Lights
• Same current (I) passes through each resistor
• Current stays the same
• Voltage drops after each resistor

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Parallel Circuit

• Different parts of circuit are on separate
  branches
• Several paths for electrons can be takes
• Ex. New Christmas Lights
• Voltage stays the same
• Current decreases through each branch

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Electrical Power

• Measure of the rate at which electricity does
  work or provides energy
• Powervoltageamperes
• Units Wattsvoltsamperes
• 1 kilowatt (kW)1000 Watts
• Electric Energy energypowertime (EPt)
• Units kilowatt-hourskilowattshours
• Your electric meter at home reads in
  kilowatt-hours this number is multiplied by
  cost/kilowatt-hr to determine your bill

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Power Distribution Grid

• At the power plant
• Generators produce 3-phase AC electricity via
  generators (electromagnetic conduction)
• Electric goes through a step-up transformer, were
  voltage is increased for travel over electric
  wires (transmission substation)
• Voltage is usually stepped up to between
  155,000-765,000 volts!

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Power Distribution Grid cont.,

• Transmission of Electricity
• High voltage lines are those huge steel towers (3
  wires for 3 phasesground)
• Electricity usually travels up to 300 miles from
  power plant
• Power Substation can do several diff. things
• Have buses split the power off into many
  directions
• Decrease the voltage by using a step-down
  transformer

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Power Distribution Grid cont.,

• Before Going Into the House
• Multi-phase wires are tapped down to single phase
  (1 wire) _at_ 120 V
• You often see three wires going to houses (single
  phase electric ground)
• Transformer drum step-down 7200 volts to 240
  volts for house
• Some neighborhoods have underground wires, so you
  might see a green transformer box (these are step
  down voltage)

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Power Distribution cont.,

• At the House
• Electric wires travel through watt-hour meter
  (charges you for electric)
• Two 120-volts wires then travel to circuit
  breaker (box in garage or basement), where its
  split and wired to all of the outlets in the house

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Magnetism
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Magnetism

• All magnets have North and South poles
• Rule for magnetic poles like poles
  repel/opposites attract
• Magnetic Fieldregion in which magnetic forces
  can act
• Earth has one around it strongest at poles
• Magnetic lines of force define these areas
• Electrons in atoms spin, causing the magnetic
  field

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Magnetic Materials

• Naturally occurring (ex. Magnetite)
• Some materials that are non-magnetized can become
  so iron, nickel are examples

Earth as a Magnet

• Magnetosphere region of magnetic field around
  the earth
• Earth poles Geographic north pole is actually
  Magnetic south pole and vice versa

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Compasses

• Needle of a compass is actually magnetic
• Compass needle points to north pole (magnetic)

Electromagnetism

• Electricity and magnetism are inseparable
• Electromagnet made by winding wire around an
  iron core
• Will have N and S poles
• Polarity of magnet depends on polarity of
  electric current
• Magnetism can induce electricity
• Electricity can induce magnetism

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Electric Motor
Electromagnets

• Electric Wire wrapped around an iron core
• These are temporary magnets can be turned on and
  off
• Ex. Junkyards, doorbells, telephones, electric
  motors

• Converts electric energy to mechanical energy
  (motion)
• Operates on the idea of reversal of polarity
• Uses a stationary permanent magnet, a rotating
  electromagnet, and a polarity-reversing switch
  (conductor)

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Galvonometer
Electric Generator

• Converts mechanical energy into electrical energy
• Loop of wire (conductor) spins inside a magnetic
  field to create electricity known as an
  elector-magnetic induction
• Most of the power you use everyday comes from
  generators

• Device that detects electric current (basically a
  coil of wire connected to an electric circuit and
  a needle)
• Current deflects needle towards direction of
  current