Domestic electricity

• What is a direct current?

  Current that flows in one direction.
• What is an alternating current?

  Current that reverses direction.
• What kind of current is supplied by cell/battery?

  Direct current.
• What kind of current is supplied by the mains?

  Alternating current.
• What is the 1) frequency and 2) voltage of the mains?

  50Hz.

  230V.
• What are the colours of the 1) live, 2) neutral and 3) earth wires?

  Live = brown.

  Neutral = blue.

  Earth = green and yellow stripes.
• What is the function of the live wire?

  Carries current to the appliance.
• What is the function of the neutral wire?

  Completes circuit, carrying current back to mains.
• Why is the live wire dangerous?

  Provides a large voltage (230V) and would cause a large current to flow through a person if touched.
• What is the function of the earth wire?

  Safety wire to stop outer casing of appliance becoming live.
• When does an earth wire carry a current?

  Only when there is a fault.
• What happens when current is carried along the earth wire and why is it dangerous?

  Resistance of earth wire is low which causes a current surge; this is dangerous as it can cause a fire.
• What is the function of a fuse?

  Fuse is a safety device; if there is a surge in current the fuse melts which breaks the circuit.
• Why do some appliances not contain an earth wire?

  Appliance is doubled insulated: the outer casing is plastic (so that casing cannot become live even if wires are loose).
• What is the National Grid?

  System of cables and transformer which delivers electrical power from power station to consumers.
• What does a step-up transformer do?

  Increases voltage (from power station to cables).
• How does increasing the voltage improve the efficiency of the National Grid?

  Increasing the voltage means a smaller current is needed to transfer the same power. smaller current means less energy is wastesas heat in cables.
• How can you calculate the wastes power lost in the cables?

  $P=$$I^2*$$R$
• What does a step-down transformer do?

  Decreases the voltage (from the cables to the consumers).
• Why is a step-down transformer needed?

  Reduces voltage to safer levels.