domestic electricity

• mains supply is...


  ac
• battery supply is...


  dc
• alternating current (ac)


  electric current that reverses its direction of flow in a regular pattern
• ac example


  fans, bulbs, air conditioners, and motors
• UK mains supply


  230V, 50Hz
• direct current (dc)


  electric current that flows in only one direction
• dc example


  batteries
• most cables have ... separate wires

  three
• three-core cables


  three wires inside them, each with a core of copper and a coloured plastic coating
• why is copper used in cable pins?

  it transports electricity more efficiently than other materials and is also resistant to corrosion and has a high thermal resistance that helps prevent overheating
• why is plastic used to cover cable pins?

  for safety as it is an electrical insulator plus it is readily available and cheap
• live wire


  brown

  - the live wire provides alternating potential difference (at around 230V) from the mains supply
• neutral wire


  blue

  - the neutral wire completes the circuit: when the appliance is operating normally, current flows through live and neutral wires. it is around 0V
• earth wire


  green and yellow

  - the earth wire is for protecting the wiring, and for safety: it stops the appliance from becoming live. it doesn't usually carry a current, only when there's a fault. it's also at 0V
• fuse


  a safety device with a thin metal strip that will melt if too much current passes through a circuit
• A fuse is connected in the ... wire

  live

  - if a high current flows and melts the fuse, the device is no longer connected to the live mains supply
• cable grip


  part of a plug that holds the cable, and stops the wires being pulled out of the pins
• cable diagram

  
• what happens when you touch the live wire?

  a large potential difference flows through you and causes a large electric shock because this would make a complete circuit from your mains supply to the ground
• a high current in a faulty appliance will flow to earth through the earth wire because this wire has a very low...

  resistance
• electric shock


  occurs when a current travels through the body to the ground rather than through electric wiring, or from static electricity that builds up on the body
• short circuit


  a connection that allows current to take the path of least resistance resulting from the unintended contact of components
• what happens if there's connection between the live and neutral wire?

  when live wire comes in contact with the neutral wire, then the insulation of wires is damaged or there is a fault in the appliance. in such a situation, the current in the circuit abruptly increases - this is known as short circuiting
• what happens if there's connection between the live and earth wire?

  when live wire comes in contact with the earth wire, then the insulation of wires is damaged or there is a fault in the appliance. in such a situation, a complete circuit would have been made from your mains supply to the ground (earth) - a shock or fire would be highly
• energy is transferred from...

  cells and other sources
• electrical appliances are designed to...

  transfer energy to components in the circuit when a current flows
• how do kettles transfer energy?

  kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle
• how do handheld fans transfer energy?

  Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan's motor.
• no appliance transfers all energy...


  completely usefully
• potential difference is...


  energy transferred per unit charge
• the higher the current...

  the more energy is transferred to the thermal energy stores if components (and then the surroundings)
• energy is supplied to the charge at the power source to...

  raise it through a potential
• energy transferred (J) =

  charge flow (C) x potential difference (V)
• energy transferred formula


  E=QV
• energy transferred formula triangle

  
• power depends on...


  current and potential difference
• power (W) =


  potential difference (V) x current (A)
• power formula


  P=VI
• power formula triangle

  
• Joule's law


  the amount of heat generated is proportional to the resistance of the wire, the time duration for which the current flows, and the square of the current flowing through the circuit