electricity

• Current

  • A measure of the flow of electrons around a circuit (electrical charge)
• Resistance

  • Every thing that resists or opposes the flow of electric charge.
  • Measured in ohms
• Resistance and potential difference

  • The greater the resistance of the component the smaller the current for a given potential difference across the component.
• Fixed resistor

  • The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference.
• Filament lamp

  • The resistance of a filament lamp increases as the temperature of the filament increases.
• Diode

  • the current through a diode only flows in one direction only.
  • Has a very high resistance in the reverse direction.
• Variable resistor

  • Modify the amount of resistance
• Thermistor

  • The resistance of a thermistor decreases as the temperature increases.
• Parallel circuit

  • The potential difference is the same cross each component
  • The total current is the sum of the the currents through. the separate components.
• Series circuit

  • Same current through each component.
  • The total potential difference is shared between the components.
  • Resistance is the sum of the resistance of the two components.
• Mains Electricity

  • Alternating current supply
  • 230V
  • Frequency of 50HZ
• Live wire

  • Brown wire
  • Carries the alternating current from the supply.
  • 230V
• Neutral wire

  • Blue wire
  • Completes the circuit
  • 0V
• Earth wire

  • Green and yellow stripes
  • A safety wire to stop the appliance becoming live.
• Step up transformer

  • Increase the potential difference from the power station to the transmission cables to decrease current.
  • Reduce energy loss
• Step down transformer

  • Decrease the potential difference for domestic use
• LED

  • Light emitting diode
  • emits light when current flows through it