P5: Electricity in the Home

• Unit of electrical power

  Watt (W)
• Formula for calculating electrical power

  P=IV
• Main purpose of a fuse in an electrical circuit

  To protect an electrical circuit by breaking the circuit if the current exceeds a safe level
• What a circuit breaker does

  Automatically breaks the circuit when the current flowing through it exceeds a predetermined level, protecting the circuit from damage
• Function of an earth wire in a plug

  Provides a path for current to flow to the ground in case of a fault, preventing electric shocks
• Colors used for live, neutral, and earth wires in a UK plug

  • Live wire: brown
  • Neutral wire: blue
  • Earth wire: green/yellow
• Difference between AC and DC

  AC (Alternating Current) changes direction periodically, while DC (Direct Current) flows in one direction only
• Why AC is used for mains electricity

  AC is more efficient for transmitting over long distances and can be easily transformed to different voltages
• Formula for calculating energy transferred in an electrical circuit

  E=Pt
• How to calculate the cost of electricity used

  Cost = Energy used (in kWh) × Cost per kWh
• Double insulation

  A safety feature where an appliance is designed with two layers of insulating material to prevent electric shock, eliminating the need for an earth wire
• Residual Current Device (RCD) and what it does

  A device that quickly breaks an electrical circuit to prevent serious harm from an ongoing electric shock, by detecting an imbalance between live and neutral wires
• Equation for calculating electrical resistance

  R=V/I
• How to calculate the current in a circuit

  I=P/V
• Purpose of using a step-up transformer in the national grid

  Increases the voltage and decreases the current for efficient transmission of electricity over long distances, reducing energy loss
• Purpose of using a step-down transformer in the national grid

  Decreases the voltage to a safer level for domestic and commercial use
• Efficiency equation for an electrical appliance

  Efficiency = (Useful power output/Total power input) × 100%