Supplying energy

• Why is the current provided by a cell called a direct current?

  Only flows in one direction
• What is an alternating current?

  A current that repeatedly reverses direction
• What kind of current is supplied by mains electricity?

  alternating current
• What is the frequency and voltage of mains electricity?

  50Hz, 230V
• What colours are the live, neutral, and earth wires in a three-core cable?

  live=brown neutral=blue earth=green
• What is the function of the live wire in a three-core cable?

  Carries alternating potential difference from the supply
• What is the function of the neutral wire in a three-core cable?

  Completes the circuit
• What is the function of the earth wire in a three-core cable?

  Safety wire
• When is there a current in the earth wire?


  When there is fault
• Why is the live wire dangerous?

  Would cause a large current to flow through a person if touched
• What is the National Grid?

  A network of cables and transformers that deliver electricity to homes and businesses.
• What are step-up transformers used for the National Grid?

  Used to increase potential difference (voltage)
• What are step-down transformers used for in the National Grid?

  Used to decrease potential difference (voltage)
• How does having a large potential difference in the transmission cables help to make the National Grid an efficient way to transfer energy?

  Large potential difference (voltage) means a small current is needed to transfer the same amount of power. Small current in transmission cables means less electrical power is wasted due to heating .
• What two things does energy transfer to an appliance depend on?

  Power of appliance, time it is switched on for
• What are the units for power, current, potential difference, and resistance?

  Watts (W) Amps (A) Volts (V) Ohms (Ω)