mains electricity

• What is a direct current (d.c.)?

  A current that flows in one direction
• How does the potential difference behave in a d.c. circuit?

  It travels in one direction only
• What does it mean for current to be only positive or negative in a d.c. circuit?

  The current does not change direction
• What type of terminals does a d.c. power supply have?

  Fixed positive and negative terminals
• What produces direct current (d.c.)?

  Electric cells or batteries
• What type of supply do circuits powered by cells or batteries use?

  A d.c. supply
• What should you remember when calculating current in d.c. circuits during exams?

  Use the same methods learned previously
• What is an alternating current (a.c.)?

  A current that changes direction continuously
• How does an a.c. power supply differ from a d.c. power supply?

  It has two identical terminals that switch
• What is the frequency of an alternating current?

  Number of direction changes per second
• What is the frequency of mains electricity in the UK?

  50 Hz
• What is the potential difference of mains electricity in the UK?

  About 230 V
• How is mains electricity characterized in terms of current direction?

  It does not have positive and negative sides
• What are the live and neutral wires in mains electricity?

  They form either end of the electrical circuit
• What is the purpose of the Earth wire?

  It is for safety
• What does the live wire do?

  It carries the alternating potential difference
• Why is the live wire considered the most dangerous?

  It carries a high voltage of around 230 V
• What is the role of the neutral wire?

  It completes the circuit with lower voltage
• What color is the live wire in the UK?

  Brown
• What color is the neutral wire in the UK?

  Blue
• What color is the Earth wire in the UK?

  Green and yellow stripes
• What safety hazard do metal cases of appliances pose?

  They can become electrified if live wire contacts
• How does the Earth wire protect against electric shock?

  It provides a low resistance path to the Earth
• What happens when a live wire contacts the Earth wire?

  A surge of current causes the fuse to melt
• What are fuses and circuit breakers designed to do?

  Cut off electricity flow if current is too large
• How does a fuse work?

  The wire melts if the current is too large
• What is a circuit breaker?

  An automatic switch that breaks the circuit
• What is an advantage of circuit breakers over fuses?

  They can be reset and used again
• Why are switches and fuses connected to the live wire?

  To disconnect the device from the live supply
• What is the potential difference of the live wire?

  Around 230 V
• What is the potential difference of the neutral wire?

  Close to 0 V
• When does the Earth wire carry current?

  Only if there is a fault in the appliance
• What is the danger of connecting live and earth wires?

  A large current can create a lethal shock
• Why do electricians switch off mains electricity when working?

  To avoid contact with live wires
• What can happen even if a device is switched off?

  The live wire can still cause an electric shock