Electrical Energy in Devices

• Energy Transfers in Appliances

  . Whenever a charge flows, it has to overcome the resistance of the circuit. This requires energy, therefore:

  - work is done when charge flows

  - the amount of work done depends on the amount of charge

  . The amount of energy transferred can also be found from the power of the appliance and how long it is used for, e.g. a 20W bulb uses 20J of energy in every second.

  . Energy transferred is measured in Joules (J), power is measured in watts (W), charge flow is measured in coulombs (C), potential difference is measured in volts (V)

  . Electrical appliances are designed to cause energy transfers

  . The type and amount of energy transferred between stores depends on the appliance
• Key Point

  The energy transferred by an appliance depends on the power and the time it is on for
• What is the National Grid?

  A system linking power stations to consumers
• What is the function of each component in the National Grid?

  Each component has a specific role in energy transfer
• What does a power station do?

  Transfers energy supply into electrical energy
• Why is using fewer large power stations more efficient?

  They can be made more efficient than smaller ones
• How do steam turbines contribute to efficiency in power plants?

  They operate more efficiently at higher steam temperatures
• Why does a larger power plant allow for higher steam temperatures?

  A bigger boiler can achieve higher steam temperatures
• What is the role of step-up transformers in the National Grid?

  They increase potential difference for transmission
• How do step-up transformers improve transmission efficiency?

  By reducing current and heating effects
• What do transmission cables do in the National Grid?

  Transfer electricity from power stations
• What is the function of step-down transformers?

  Reduce potential difference for domestic use
• Key Point

  Electrical power is produced and transferred efficiently to consumers using the National Grid
• What is the voltage transformation process in the National Grid?

  • Power Station: 25,000V
  • Step-up Transformer: Increases to 400,000V
  • Transmission Cables: Carry electricity at 400,000V
  • Step-down Transformer: Reduces to 230V
  • Domestic Use: Houses, shops, etc. at 230V