Mains electricity

• What is the process called that transfers energy from one store to another?

  Pathway
• What is mechanical work defined as?

  Force moves an object a distance
• What does electrical work involve?

  Charges moving due to a p.d.
• What causes heating in energy transfer?

  Temperature difference
• How is radiation transferred?

  As a wave, e.g., light
• What are the characteristics of direct current (DC) and alternating current (AC)?

  • DC: Current supplied by a battery
  • AC: Voltage constantly changes direction
  • AC: Current supplied by UK mains
  • DC: Voltage has a constant direction
• What does an oscilloscope display for direct current?

  Straight line, current moves in one direction
• What does an oscilloscope display for alternating current?

  Wave trace, current changes direction
• What is the frequency of mains electricity?

  50Hz
• What does the live wire carry?

  Voltage to the electrical device
• What is the role of the neutral wire?

  Completes the circuit
• What is the function of the earth wire?

  Ensures the device is safe
• What is the potential difference (p.d.) between the live wire and the other two wires?

  230V
• What happens if the earth and live wires touch?

  Causes a short-circuit and overheating
• What is the formula for power?

  Power = potential difference x current
• How is potential difference (V) calculated?

  V = P ÷ I
• How is current (I) calculated?

  I = P ÷ V
• What are the units for power, potential difference, and current?

  Power: Watts (W), Voltage: Volts (V), Current: Amperes (A)
• What are the hazards associated with electricity?

  • Frayed cables
  • Long cables (tripping hazard)
  • Damaged plugs
  • Water around sockets
  • Pushing conductors into sockets
• What safety measures are used with electrical devices?

  • Plastic casing on wires
  • Earthed metal cases
  • Fuses to break circuits
  • Circuit breakers to switch off current
  • Double insulation for devices
• What happens when a fault develops in a device with a metal case?

  Large current flows through the earth wire
• What is the purpose of a fuse?

  Protects device from overheating
• What sizes of fuses are available?

  5A, 10A, 13A
• What does double insulation mean?

  Plastic case that cannot become hot
• How does a circuit breaker differ from a fuse?

  Can be reset after a fault
• What are the colors of wire insulation?

  Brown (live), blue (neutral), green & yellow (earth)
• What is electrocution?

  Injury or death from electric shock
• What are the benefits of circuit breakers over fuses?

  • Acts more quickly
  • More reliable
  • Can be reset
  • More sensitive
• What happens when a current flowing heats a wire?

  Can be helpful or cause overheating
• What can stop current flow to prevent damage?

  Switches, fuses, circuit breakers
• What happens to resistance when the temperature of a metal conductor increases?

  Resistance increases due to more collisions
• What is the behavior of a thermistor as temperature increases?

  Resistance decreases as temperature increases
• How can resistance be reduced in electrical circuits?

  Using low resistance wires