mains

• three pin system


  blue wire = neutral wire

  brown wire = live wire

  green/yellow wire = earth wire

  13A fuse is connected to the live wire

  where the cable enters the plug, there is a cable grip
• what are fuses?

  fuses are a safety feature which are connected between the live pin and the live wire, the wire inside melts if the current gets too high. the current rating is the max current they can carry. common values are 1A, 3A, 5A and 13A.
• residual current circuit breakers


  circuits in a house have a 13A fuse connected to them. now, RCCBs are used instead. an RCCB is an electromagnetic switch which acts like a fuse. if the current gets too big it trips the RCCB, they're re-settable and act quicker than fuses. the also can disconnect a whole circuit and not just an appliance.
• energy diagrams


  filament lamp = electrical -> light + heat

  motor = electrical -> kinetic + thermal + sound

  loud speaker = electrical -> kinetic + sound + thermal

  heater = electrical -> thermal + sound + light

  microphone = sound -> electrical
• in ac supplies, the current is constantly changing direction. alternating currents are produced by alternating potential difference where the positive and negative ends keep alternating
• direct current always flow in the same direction, the potential difference is direct.
• the uk mains supply is an ac supply as around 230Hz
• the frequency of the ac mains supply is 50Hz
• what is the live wire?

  the live wire is brown and provides the alternating potential difference from the mains supply.
• what is the neutral wire?

  the neutral wire is blue and this completes the circuit. when the appliance is operating normally, current flows through the live wire and neutral wire.

  it is around 0V
• what is the earth wire?

  the earth wire is green and yellow

  it stops the appliance from becoming live. it does not carry a current until there is a fault. it is also at 0v. the earth pin is the longest so when it comes into contact with the socket, it is already earthed.
• power = potential difference x current
• E = QV

  E - energy

  Q - charge

  V - potential difference