mains electricity

• What are the two types of electric current?

  Direct current and alternating current
• How does direct current flow?

  A direct current flows in only one direction
• What devices provide direct current?

  Car batteries, dry cells, and solar cells
• What does a direct current signal look like on an oscilloscope?

  It appears as a horizontal straight line at a constant voltage
• How does alternating current differ from direct current?

  An alternating current regularly changes direction
• What does an alternating current signal look like on an oscilloscope?

  It appears as a 50Hz sine wave that peaks at 230V
• What is the frequency of the mains electrical supply in the UK?

  50 Hertz (Hz)
• What voltage is the mains electrical supply delivered at in the UK?

  230 Volts (V)
• What are the functions of the components inside a plug?

  • Outer insulation: Bundles wires for safety
  • Cable grip: Holds the cable tightly
  • Live wire: Carries current into the device
  • Fuse: Melts if current is too high
  • Neutral wire: Completes the circuit
  • Earth wire: Provides a path to ground in case of fault
• Why is the earth wire important in electrical appliances?

  It provides a low resistance path to the ground in case of a fault
• What happens if the live wire becomes loose without an earth wire?

  There is a danger of electrocution if someone touches the appliance
• How does a fuse protect electrical devices?

  A fuse melts if the current gets too high, breaking the circuit
• What is the equation to calculate energy transferred by an appliance?

  energy = power × time
• What units are used to measure energy, power, and time?

  Energy in joules (J), power in watts (W), time in seconds (s)
• How should time be converted when calculating energy?

  Time should be converted from minutes into seconds by multiplying by 60
• How much energy is transferred by a 1,500 W hair dryer in 15 minutes?

  Energy = 1,500 W × (15 × 60 s) = 1,500 W × 900 s = 1,350,000 J
• What is the power of an electric heater that draws a current of 8 amps when plugged into the mains?

  Power = 230 V × 8 A = 1,840 W
• How much energy is transferred by the electric heater used for 20 minutes?

  Energy = 1,840 W × (20 × 60 s) = 1,840 W × 1,200 s = 2,208,000 J
• What is the National Grid and its function?

  • Distributes electricity across the country
  • Connects power stations to homes and buildings
  • Electricity can be produced by various methods
• What is the purpose of transformers in the National Grid?

  Transformers change voltages and currents in transmission lines
• How does a step-up transformer function?

  It increases voltage and decreases current
• What is the relationship between voltage and current in power transmission?

  Increasing voltage decreases current and vice versa
• Why are pylons used in the National Grid?

  Pylons support transmission lines above the ground for safety
• What happens to transmission lines as electric current flows through them?

  They get hotter and dissipate energy to the surroundings
• What is the equation for power dissipation in transmission lines?

  power = current² × resistance
• How can power loss in transmission lines be minimized?

  By using thick cables and high voltages to reduce current
• What is the benefit of low resistance and low current in transmission wires?

  It prevents the wires from heating up and losing power