electricity

• why is the current provided by a cell called a direct current (dc)?


  only flows in one direction
• what is alternating current (ac)?


  current that repeatedly reverses direction
• what kind of current is supplied by mains electricit?


  Alternating current
• what is the frequency and voltage of mains electricity

  50Hz , 230V
• what colours are the live, neutral and earth wire

  live - brown

  neutral - blue

  earth - green & yellow stripes
• what is the function of the live wire

  carries the alternating p.d from the supply
• what is the function of the neutral wire

  completes the circuit
• what is the function of the earth wire

  safety wire to stop the appliance becoming live
• when is there a current in the earth wire

  when there’s a fault
• why is the live wire dangerous

  provided a large p.d that would cause a large current to flow through a person if they touched it
• what is the national grid

  nationwide network of cables and transformers that link power stations to customers
• what are step up transformers in the national grid

  increase the p.d from the power station to the transmission cables
• what are step down transformers used in the national grid

  decrease p.d from the transmission cables to the mains supply in buildings so that it is safe to use
• how does having a large p.d in the transmission cables help to make the national grid an efficient way to transfer energy

  large p.d means a small current is needed to transfer the same amount of power small current in the transmission cable means less electrical powers wasted due to heatinf
• what two things does energy transfer to an appliance depend on

  power of appliance

  time it’s on for
• charge flow equation?

  charge flow = current x time
• energy transferred equation?

  energy transferred = charge flow x p.d
• power (current) equation?


  power = current x p.d
• power (energy) equation?

  power = energy / time