Power and Electricity in the Home

  • Created by: India.02
  • Created on: 01-05-19 20:52
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  • Power and Electricity in the Home
    • Mains Supply
      • The UK mains supply is an ac supply at around 230V
        • In ac supplies, the current is constantly changing direction - produced by alternating potential difference in which the positive and negative ends keep alternating
      • The frequency of the ac mains supply is 50 cycles per second or 50 Hz
      • Cells and batteries supply direct current - dc
        • Direct current is a current that is always flowing in the same direction - created by a direct potential difference
      • Cables
        • Appliances connected to mains supply by three-core cables - each with a copper core and a coloured plastic coating
        • Neutral wire - blue - completes the circuit and carries the current away - electricity normally flows in through the live wire and out through the neutral wire - around 0V
        • Live wire - brown - provides alternating potential difference (230V) from the mains supply
        • Earth wire - green and yellow - stops appliance becoming live - doesn't usually carry current - only when there is a fault - around 0V
    • Power
      • Power of an appliance is the energy that it transfers per second
        • Appliances often given a power rating - labelled with maximum safe power they can operate at - maximum operating power
          • Tells you the maximum amount of energy transferred between stores per second when the appliance is in use
            • Helps customers choose between models - lower power rating means that less electricity is used in a given time - cheaper to run
        • Higher power doesn't necessarily mean that it transfers more energy usefully - more powerful than another but less efficient - still only transfer the same amount of energy to the useful stores
      • Equations
      • Transfer from Cells
        • A moving charge transfers energy - charge does work against the resistance of the circuit
          • No appliance transfers all energy completely usefully - higher the current, the more energy transferred to the thermal stores of the components
        • Kettles transfer energy electrically from mains supply to thermal store in the heating element of the kettle
        • Energy is transferred electrically from the battery of a handheld fan to the kinetic store of the fans motor
          • No appliance transfers all energy completely usefully - higher the current, the more energy transferred to the thermal stores of the components
    • Energy Transferred
      • When an electrical charge goes through a change in potential difference, energy is transferred
        • A battery with a bigger p.d. will supply more energy to the circuit for every coulomb of charge which flows around it - the charge is raised up 'higher' at the start
      • Energy is supplied to the charge at a power source to 'raise' it through a  potential
        • The charge gives up this energy when it 'falls' through any potential drop in components elsewhere in the circuit

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