ELECTRICITY

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ELECTRICITY MAGNETISM

• UNIT 56

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Electricity and Magnetism

• Both are derived from a single, fundamental kind
  of force- electromagnetic force.
• All electric and magnetic properties come form
  the most fundamental particles in the world,
  protons and electrons which make up atoms.

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Electricity Electric Charge

• An electrical charge is an electrical property of
  matter that creates a force between 2 objects. SI
  unit is c (coulomb)
• Like charges repel and opposite charges attract
• An objects electric charge depends on the
  imbalance of its protons and electrons.

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Protons and Electrons

• Electron spin produces a tiny magnetic field
  around every electron.
• Protons are positively charged ().
• Electrons are negatively charged (-).
• One proton balances out one electron.

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Electric Force

• Charges exert forces push or pull
• Attraction forces oppositely charged particles
• Repulsion forces particles with the same charge
• Like charges repel unlike charges attract

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Electric Fields

• The area around every charged particle
• Are strongest near the charged particle
• Depends on charge and distance
• Field lines can not cross
• Any charged object that enters a region with an
  electric field experiences an electric force

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Conductors Insulators

• Conductors have low resistance and allow
  electrons to move freely throughout them.
• Super conductors metals and compounds that have
  zero resistance when the temperature falls below
  a critical temperature.
• Insulators have high resistance to charge
  movement.

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Transfer of Electric Charge

• Objects can be charged by the transfer of
  electrons.
• Charges move within uncharged objects.

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Static Electricity

• Transfer of electrons by friction.
• Movement a friction opposes movement a creates an
  electric charge static electricity
• Static discharge release of a buildup of
  charges

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Benjamin Franklin

• Lightning is a natural method of producing
  electricity.
• Benjamin Franklin was the first to capture the
  electrical current from a lightning storm using a
  wire as a kite tether.
• He invented the lightning rod.

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Charging Objects Without Friction

• Touch an object with another charged object
  charge by contact or conduction
• Induced charge charges in a neutral conductor
  can be redistributed without contact, bring
  charged object close and the charges in the
  neutral object will realign (opposites attract)

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Bonding and Grounding

• When you move flammable liquid from one container
  to another, get build up of charges due to
  friction from movement of liquid.
• Bonding equalize charges on each side. Ex gas
  pump
• Ground removal of excess charges. Ex pump is
  grounded

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Current

• The rate that electric charges flow through a
  wire or any conductor. SI unit is (I), amperes
  or amps.
• DC Direct Current
• Current that flows in one direction from positive
  to negative charged areas.
• AC Alternating Current
• Current that flows back and forth, alternating
  direction of flow.

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Voltage

• Measure of the potential difference between tow
  places. SI unit is (V), volts.
• Potential difference is the force that causes
  electrons to flow in a circuit.
• 1 volt 1 joule / coulomb
• Watts voltage amps

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Resistance

• The tendency for a material to oppose the flow of
  electrons. SI unit is (R), ohms.
• Thin wires have a greater resistance to electron
  flow than do thicker wires.
• In a light bulb the lower the watt the higher the
  resistance.

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Ohms Law

• Current flowing in a metal conductor is directly
  proportional to the potential difference and
  inversely proportional to the resistance.
• The more voltage (potential difference), the
  faster the current flows
• The more resistance, the slower the current flows.

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Formula for Ohms Law

• Current Voltage / Resistance
• I V/R
• V
• I R
• V voltage (volts)
• I current (amperes)
• R resistance (ohms)

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Cells

• A device that is a source of electric current
  because of a potential difference or voltage
  between a positive and negative terminal.
• Dry cell contains a gel-like acid in a zinc case
  and a carbon rod releases electrons and becomes
  the positive terminal. Ex household battery
• Each dry cell produces 1.5 volts
• Wet cell usually has lead plates surrounded by
  sulfuric acid. Ex car battery
• Each wet cell produces 2 volts

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Alessandro Volta

• He was an Italian physicist who invented the
  battery thus the term "Volt", meaning electrical
  potential.
• In 1791, Volta was experimenting with metals and
  acids and was able to assemble a pile of cells to
  form a battery. He touched a silver spoon and a
  piece of tin to his tongue (saliva is slightly
  acidic) and connected them with a piece of copper
  wire. He experienced a "sour" taste, and realized
  he was experiencing an electrical
• phenomenon. Each cell was a disk of zinc and a
  disk of silver, separated by a layer of
  brine-soaked pasteboard.
• We now refer to that original battery as a
  Voltaic Pile.
• In Volta's honor, we refer to electrical pressure
  as "Voltage.

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Electric Circuit

• Path through which charges can be conducted.
• When a device is connected there must be a
  complete path for charges to move.
• Electrons move from the terminal through the
  wire and back to the terminal.
• The path must be closed.

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Simple Electrical Circuit

• A flashlight is a good example of a simple
  electrical circuit.
• A flashlight has a battery (source), wires
  connected to the battery (conductor), the
  (switch) activated by the thumb of the hand
  holding the flashlight, and the bulb in the head
  of the flashlight is the (load).
• A load, in order to perform it's task, must have
  the proper voltage applied. The voltage is
  carried to the load with the conductor and the
  switch controls the flow of the current to the
  load.
• When the switch is "open" no light will shine.
  With the switch "closed the light will shine.
• If the light bulb is burned out  the resistance
  to the current flow will be so great
  (increasing), it will prevent the flow of
  current. When the voltage remains the same and
  the resistance increases, the watts (amount of
  light) decreases. In this case, no current will
  flow, which causes no light to shine.

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Open and Closed Circuits

• When the path is closed it is a closed circuit
  and electrons can make a complete circuit.
• When there is not a complete loop electrons cant
  flow and it is called an open circuit.
• When a switch is added it can open and close the
  circuit causing the device in the circuit to work
  and stop working.

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Schematic diagram

• Used to represent circuits.
• Graphic representation of an electric circuit or
  apparatus, with standard symbols for the
  electrical devices.
• Standard symbols are used that are recognized
  world wide.
• Site with schematics explained

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Circuits in Series

• Single path for current.
• Current is always the same.

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Parallel Circuits

• Multiple paths for current.
• Voltage is always the same.

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What are these circuits?
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Electric Power Energy

• Electrical power is the rate at which electrical
  energy is used in a circuit.
• Electrical energy is the energy associated with
  electrical charges, they can be moving or
  resting.
• Electric companies measure energy consumed in
  kilowatts/hour.
• P power (watts)
• P I current (amperes)
• I V V voltage (volts)

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Fire Danger

• Overloaded circuit when the current being drawn
  across a circuit is more than the circuit can
  handle. Ex too many appliances are plugged in
• Short circuit when wires touch and create an
  alternative pathway for current. Ex worn
  insulation on wires
• GFCI ground fault circuit interrupt grounded
  outlet will turn off. Ex in kitchen or bathroom

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Fuses Circuit Breakers

• Fuses melt to prevent circuit overloads.
• Circuit breakers open with high current. They
  act as a switch.
• Most homes today have circuit breakers instead of
  fuses. You will find fuses in cars and Christmas
  lights.

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Magnetism

• Property of matter in which there is a force of
  attraction or repulsion between like and unlike
  poles.
• Permanent magnets are made form iron, cobalt, and
  nickel because they keep their magnetic fields
  for a long time.
• In an unmagnetized object the atoms domains are
  randomly arranged and in a magnetized object the
  atoms domains are all arranged in the same
  direction.
• Experiments

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Magnets

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Did You Know?

• The first magnets ere found in Magnesia, Greece.
• A natural occurring magnetic rock is known as a
  lodestone.
• This rock is made of an iron material called
  magnetite.

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Michael Faraday

• In 1831 he discovered that current can be
  produced by pushing a magnet through a coil of
  wire. As the loop of wire (conductor) moves in
  and out of the magnetic field a current is
  induced.
• Faradays Law an electric current can be produced
  in a circuit by rotating a conductor through a
  magnetic field.

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Magnetic Fields

• Region around the magnet where magnetic forces
  act. Represented by flux lines which always
  point from magnetic north to magnetic south.
• A compass tracts a magnetic field.
• The earth is a giant bar magnet.

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Earth is a Magnet

• Earth is a giant bar magnet with a north and a
  south magnetic pole.
• The magnetic pole in the geographical north is
  actually the magnetic south pole.
• The magnetic field around the earth is created by
  the spinning molten metals at the earths center.
  This spin is the opposite of the earths rotation.

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Types of Magnets

• Hard magnet (Ni, Co) hard to magnetize but
  stays magnetized.
• Soft magnet (Fe) easy to magnetize but doesnt
  stay magnetized.

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Magnetic Information

• Dropping any magnet weakens it because domains
  start to unalign.
• Breaking a magnet in two makes two magnets.
• Heating a magnet weakens it because it increases
  thermal dynamic motion.
• Magnetic induction is magnetizing another object
  by bringing it in close contact with a permanent
  magnet.

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Current Magnetism

• Electric currents produce magnetic fields.
• The magnetic field of a coil of wire resembles
  that of a bar magnet.
• Force causes the needle to turn in the direction
  of the wires magnetic field.

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Right Hand Rule

• Use the right hand rule to find the direction of
  the magnetic field produced by a current.
• If you imagine holding a wire in your right hand
  with your thumb pointing in the direction of the
  positive current, the direction your fingers
  point is the direction of the magnetic field.

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Producing Electric CurrentGenerators

• Most of the current used in homes today is
  produced by generators using electromagnetic
  induction.
• Electromagnetic induction is the process of
  producing electric current by moving a wire in
  and out of a magnetic field.
• Generators produce Alternating Current by causing
  the coils of wire to slide form one pole to the
  other causing the current to reverse itself at 60
  cycles/second.

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Electric Utilities

• 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 generate electricity. Steam turbines,
  internal-combustion engines, gas combustion
  turbines, water turbines, and wind turbines are
  the most common methods to generate electricity. 
  Most power plants are about 35 percent efficient.
  That means that for every 100 units of energy
  that go into a plant, only 35 units are converted
  to usable electrical energy.
• Most of the electricity in the United States is
  produced in steam turbines. 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.

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Turbine Generator

• Diagram of a turbine generator
• Steam is the usual source of energy with
  different ways of producing steam.

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Explanation Using Hydropower Plant

• Hydropower plant dam built to harness power of
  falling water a moves blades or turbine a
  attached to a core wrapped with loops of wire
  that rotate within a strong magnetic field a
  generates electricity.

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• Coal power plant burns a heats water to a steam a
  turns fan a attached to core wrapped with loops
  of wire that rotate within a strong magnetic
  field a electricity
• Nuclear power plant uses the heat from U235 to
  heat water into steam

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Electromagnets

• Electromagnets are created when current moves
  through a wire creating a magnetic field around
  the wire and iron or steel it is contact with.
  The field is strengthened when the wire is wound
  around the metal in coils.
• Used to produce sound, pick up heavy objects,
  generating electricity.

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Solenoids

• Long, wound coil of insulated wire.
• Magnetic field of each loop of wire adds to the
  strength of the magnetic field of the loop next
  to it.
• The strength of the magnetic field of a solenoid
  depends on the number of loops of wire and the
  amount of current in the wire.
• An electromagnet is a strong magnet created when
  an iron core is inserted into the center of a
  current carrying solenoid.

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Electromagnetic Wave

• Both the electric and magnetic fields are
  perpendicular to the direction that the wave
  travels.

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Galvanometer

• Used to measure current and voltage
• Consists of a coil of wire wrapped around an iron
  core that can spin between the poles of a
  permanent magnet
• When attached to a circuit the needle moves
  across the scale

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Electric Motors

• Convert electric energy to mechanical energy.
• Current in the coil produces a magnetic field
  that interacts with magnetic field of surrounding
  magnet causing coil to turn

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Continued on next slide
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Transformers

• Magnetic field produced by a primary coil induces
  a current in a secondary coil.
• Voltage across the secondary coil is proportional
  to the number of loops or turns in the wire
  relative to the number of loops in the primary
  coil.

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Step up and Step down Transformers

• To provide continuous current and voltage to each
  home the power company has to continually step up
  the voltage along power lines. Large
  transformers are positioned on power poles along
  the distribution lines. These give homes at the
  end of the distribution lines enough voltage to
  power appliances and lights.
• Step down transformers lower the voltage from
  outlets to levels household appliances can use.

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Diagram of Transformers at Work
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Review

• Good overall review not all pages are finished
• Famous people
• Definitions
• Energy kids page
• Basic information
• YouTube

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