Current electricity

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  • Created by: Holly45
  • Created on: 23-03-15 19:51

Parallel circuits

  • each component is separatly connected to the positive and negative of the supply
  • if you disconnect one of the components it will hardly affect the others
  • all the components get a full source of voltage so the voltage is the same all the way across (V1 = V2 = V3)
  • the total current is equal to the total of all the currents though the separate components (A = A1 + A2 + A3)
  • there are junctions where the current splits and rejoins
  • the total current going into a junction has to equal the total current leaving
  • ammeters are always connected in series even in a parallel circuit
  • voltmeters are always connected in parallel even in series
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Series circuits

  • connect in a line between the negative and positive of the power supply
  • if you remove or disconnect one component the circuit is broken
  • the total P.d of the supply is shared between the various components
  • the voltage around a series circuit always adds up to equal the sources voltage (V = V1 + V2 + V3)
  • the same current flows through all parts of the circuit (A1 = A2)
  • the total resistance is the sum of all resistances (R = R1 + R2)
  • the bigger the resistance of a component then there is a bigger share of the total P.d
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Circuit devises

  • current only flows though a diode in one direction
  • light emitting diodes are useful and they only have a small current
  • an LDR is a resistor that is dependant on light
  • the resistance of a thermistor decreases as the temperature increases
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  • voltage and current graphs show how the current varies as you change the potential difference
  • filament lamp graph shows as the temperature increases the resistance increases
  • a diode only lets the current flow in one direction
  • resistance increases with temperature
  • P.d = current X resistance (V = I x R)
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  • the ammeter measures the current flowing though the component and must be placed in series
  • the voltmeter measures the potential difference and must be placed in parallel
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Current and potential difference

  • current is the flow of electrical charge
  • it will only flow if there is a potential difference across it
  • potential difference is the force that pushes the current around
  • resistance is anything in the circuit which slows the flow down
  • the greater the resistance, the smaller the current flows
  • current = charge (divided by) time (Q = I x T)
  • potential difference across an electrical component is the energy that is transferred by the electrical component per unit of charge
  • P.d = work done (divided by) charge
  • W = V x Q
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Static electricity

  • caused by friction
  • when insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other
  • this leaves a positive static charge on one and a negative charge on the other
  • electricity charged objects attract small objects placed near them
  • both negative and positive electrostatic charges are only ever produced by the movement of electrons
  • positive charges are caused by electrons moving away
  • two things with opposite electrical charges are attracted to each other
  • electrical charges can move easily though some metals known as conductors
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