Mains Electricity

• AC


  Alternating current, where the current continuously varies from positive to negative
• DC


  Direct current, the movement of charge in one direction only
• Components of a plug

  • Live wire
  • Neutral wire
  • Earth wire
• Live wire


  • Carries the alternating potential difference from the mains supply at 230V
  • May be dangerous even if the mains circuit is switched off as current may still be flowing through it
• Neutral wire


  • Completes the circuit at 0V
• Earth wire


  • Safety wire to stop the appliance becoming live if the live wire touches the metal casing
  • Connected to the earth and to the casing
• Power


  The energy transferred per second, directly proportional to current and voltage
• Power loss


  Proportional to resistance and the square of the current
• Electrical energy may be transferred by the appliance in different ways: kinetic energy for a motor, thermal energy in a kettle</b>
• Work done is when charge flows through a circuit, and is also equal to energy transferred, as all the electrical energy (ideally) gets transferred to the appliance
• Power rating of an appliance shows the power it uses in Watts, so greater power rating means it uses more energy
• National Grid


  • System of cables and transformers linking power stations to consumers across the UK
  • Electrical power is transferred from power stations to consumers using the National Grid
• Step-up Transformers


  • Increase the potential difference from the power station to the National Grid, so as the power is constant current decreases so less energy is lost
• Step-down Transformers


  • Decrease the potential difference from the National Grid to consumers, for consumer safety