Energy Transfer

• Power


  The rate at which energy is transferred or converted.

  Units: Watts (W)
• Power = current x potential difference (P = IV)
• Power = (current)^2 x Resistance
• Electrical Energy Transfers


  Everyday electrical appliances are designed to bring about energy transfers
• Amount of energy an appliance transfers


  • Depends on how long the appliance is on (time)
  • Depends on the power rating of the appliance
• Appliances transfer energy electrically


  • From batteries (if battery powered)
  • From the AC mains (if needs to be plugged in)
• Appliances and their energy transfers

  • ELECTRICAL ENERGY
• Work is done


  When charge flows through a circuit
• Calculating the amount of energy transferred by electrical work


  E = P * t
• Another way to express energy transferred


  E = Q * V
• Power Rating


  Every electrical appliance has a power rating which tells you how much energy it needs to work
• High-power appliance like a toaster

  Uses more energy in a shorter amount of time compared to a low-power appliance like a clock
• Electrical Tranfer

  A) power station

  B) national grid

  C) consumer

  
• Transformer Equation

  A) current in primary coil

  B) potential difference across secondary coil

  C) current in secondary coil

  
• National Grid


  A large network consisting of cables and transformers that connects power stations to consumers, distributing electricity across the country
• National Grid


  • Operates using a high potential difference (PD) and a low current to transmit electricity efficiently
  • A high current would lead to a significant amount of energy being lost as heat in the cables, so it's avoided by using a high potential difference which allows for a low current
  • A lower current reduces energy loss and prevents the wires from heating up too much, making the grid more efficient
• Transformers


  Used to change the potential difference for efficient energy transmission over long distances
• Types of transformers


  • Step-up transformers
  • Step-down transformers
• Step-up transformers


  Increase the potential difference and decrease the current
• Step-down transformers


  Decrease the potential difference and increase the current
• Electricity transmission


  1. Power station

  2. Step-up transformer (increases PD, decreases current)

  3. Long distance transmission

  4. Step-down transformer (decreases PD, increases current)

  5. Consumer
• Transformers are made up of two coils of wire, called the primary and secondary coils, around a magnetic iron core
• The power transferred by a transformer is almost equal in the primary and secondary coils
• There is a transformer equation that can be derived from the fact that the power transferred is almost equal in the primary and secondary coils