Physics P5

• What is the definition of alternating current?

  Current that reverses direction periodically
• What does alternating potential difference refer to?

  Voltage that changes direction periodically
• What is charge flow?

  Movement of electric charge through a circuit
• What is direct current?

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

  Voltage that remains constant in one direction
• What is the National Grid?

  A network linking power stations to consumers
• What unit is used to measure charge?

  Coulombs
• What is a short circuit?

  A fault causing excessive current flow
• What is a step-down transformer?

  A device that decreases potential difference
• What is a fuse?

  A safety device that prevents overload
• What is a step-up transformer?

  A device that increases potential difference
• What are the characteristics of mains electricity in the UK?

  • Provides alternating current (AC)
  • Frequency: 50 Hz
  • Voltage: 230 V
• 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 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 benefit power transfer?

  It reduces the current needed for power
• 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 advantages of using a high potential difference in the National Grid?

  • Reduces current needed for power transfer
  • Minimizes heating loss in cables
  • Increases efficiency of energy transfer
• What type of cable connects most electrical appliances in the UK?

  Three-core cable
• Why is copper used for wires in electrical appliances?

  It is a good electrical conductor
• Why is plastic used for wire coatings and plug cases?

  It is a good electrical insulator
• What is the role of the neutral wire?

  Completes the circuit with 0V potential
• What is the purpose of the Earth wire?

  Prevents appliances from becoming live
• What happens during a short circuit?

  A large current flows due to a fault
• Why is the live wire considered dangerous?

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

  • Convert energy from one form to another
  • Example: Hairdryer transfers chemical to kinetic and thermal energy
• What causes charge to flow through an electrical appliance?

  The potential difference of the mains supply
• How can you calculate charge flow?

  Charge flow (C) = Current (A) × Time (s)
• How can you find energy transferred to an electrical appliance?

  Energy (J) = Charge flow (C) × Potential difference (V)
• What is the formula for energy transferred by an electrical appliance?

  Energy (J) = Power (W) × Time (s)
• What is the relationship between primary and secondary potential difference and current in transformers?

  • Primary potential difference × Primary current = Secondary potential difference × Secondary current
  • Formula: $V_p I_p =$$V_s I_s$
• Why is the National Grid efficient for power transfer?

  • Higher potential difference reduces current
  • Less heating loss in wires
  • Assumes 100% efficiency
• What is the main advantage of using a high potential difference in the National Grid?

  It reduces heating loss in wires
• What is the potential difference of the Earth wire?

  0V
• What happens to the fuse during a short circuit?

  The fuse melts and disconnects the live wire
• What is the potential difference of the neutral wire?

  0V
• How does the National Grid connect power stations to consumers?

  Through a network of cables and transformers
• What is the role of the live wire in an electrical appliance?

  It carries high potential difference of 230V