Power of Electrical Appliances

• Electrical circuits


  Energy transfer - the charge carriers take energy around the circuit. When they go through an electrical component energy is transferred to make the component work.
• Energy transfer from cells and other sources

  1. Charge transfers energy because it does work against the resistance of the circuit

  2. Electrical appliances are designed to transfer energy to components in the circuit when a current flows
• Energy transfer in electrical appliances

  • Kettles transfer energy electrically from the mains AC supply to the thermal energy store of the heating element
  • Handheld fan transfers energy electrically from the battery to the kinetic energy store of the fan's motor
• No appliance transfers all energy completely usefully. The higher the current, the more energy is transferred to the thermal energy stores of the components (and then the surroundings).
• You can calculate the efficiency of any electrical appliance
• Power of an appliance


  The energy that it transfers per second
• Appliances are often given a power rating - the maximum safe power that they can operate at
• The power rating tells you the maximum amount of energy transferred between stores per second when the appliance is in use
• A higher power doesn't necessarily mean that it transfers more energy usefully. An appliance may be more powerful than another, but less efficient, meaning that it might still only transfer the same amount of energy (or even less) to useful stores.
• Potential difference


  Energy transferred per charge passed
• A battery with a bigger potential difference will supply more energy to the circuit for every coulomb of charge which flows round it, because the charge is raised up "higher" at the start.