P5 Electricity in the Home

• What is the definition of alternating current?

  Current that reverses direction periodically
• What is the definition of alternating potential difference?

  Voltage that changes direction periodically
• What does charge flow refer to?

  Movement of electric charge in a circuit
• What are coulombs?

  Units of electric charge
• What is the definition of direct current?

  Current that flows in one direction only
• What is direct potential difference?

  Voltage that does not change direction
• What is a fuse?

  Device that protects circuits from overload
• What is the National Grid?

  Network linking power stations to consumers
• What is a short circuit?

  Unintended low-resistance connection in a circuit
• What is a step-down transformer?

  Device that decreases voltage in a circuit
• What is a step-up transformer?

  Device that increases voltage in a circuit
• What are the characteristics of mains electricity?

  • Provides alternating current (AC)
  • Voltage is 230 V
  • Frequency is 50 Hz
• Why do transformers improve efficiency in the National Grid?

  They change potential difference for power transfer
• What potential difference do power stations generate electricity at?

  About 25000 V
• What potential difference do transmission cables transfer electrical power at?

  Up to 400000 V
• What potential difference do homes and offices use?

  230 V
• How does a high potential difference across transmission cables improve efficiency?

  It reduces current needed for power transfer
• What is the formula for power in terms of current and potential difference?

  Power (W) = Current (A) × Potential Difference (V)
• What is the formula for power loss in heating a cable?

  Power (W) = Current² (A) × Resistance (Ω)
• What are the components of a three-core cable?

  • Live wire: brown, carries potential difference
  • Neutral wire: blue, completes circuit
  • Earth wire: green/yellow, safety wire
• 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 to prevent live appliances
• When does the earth wire carry current?

  Only when there is a fault
• Why is the live wire considered dangerous?

  It has a high potential difference of 230 V
• How do electrical appliances transfer energy?

  • Transfer energy from chemical store to kinetic energy
  • Example: Hairdryer converts energy to heat and motion
• What causes charge to flow through an electrical appliance?

  The potential difference of the mains supply
• What is the formula for charge flow?

  Charge flow (C) = Current (A) × Time (s)
• What type of current does a cell or battery provide?

  Direct current (dc)
• How does direct current (dc) flow?

  It flows in one direction only
• What is the formula for energy transferred to an electrical appliance?

  Energy transferred (J) = Charge flow (C) × Potential difference (V)
• What type of current does mains electricity provide?

  Alternating current (ac)
• What is the formula for energy transferred by an electrical appliance?

  Energy transferred (J) = Power (W) × Time (s)
• What happens to the current in alternating current (ac)?

  The current repeatedly reverses direction
• What is the frequency of mains electricity supply in the UK?

  50 Hz
• What is the relationship between primary and secondary potential difference and current in transformers?

  Vp Ip = Vs Is
• What is the voltage of mains electricity in the UK?

  230V
• How does a higher potential difference in the National Grid improve efficiency?

  It reduces current needed, minimizing heating loss
• What is the purpose of the Earth wire?

  To stop the appliance becoming live
• What is the potential difference of the Earth wire?

  0V
• What are the units for power, current, potential difference, and resistance?

  • Power: watts (W)
  • Current: amps (A)
  • Potential difference: volts (V)
  • Resistance: ohms (Ω)