Energy transfers

• State two equations for the power of a circuit

  1. P = I V

  2. P = I² R
• State an equation linking energy transferred, power and time

  E = P t
• State an equation linking energy transferred, charge flow and potential difference

  E = Q V
• Amount of energy transferred by an appliance depends on

  • How long the appliance is being used for
  • The power of the appliance
• Describe the energy transfers in a battery powered torch

  1. Battery converts chemical energy into electrical energy

  2. Bulb converts electrical energy into light as well as waste energy in the form of heating
• Describe the energy transfers in a battery powered motor

  1. Battery converts chemical energy into electrical energy

  2. Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
• What three things determine the power of a circuit device

  • The potential difference across the circuit
  • The current through the circuit
  • The amount of energy transferred in a given time
• National Grid


  To link power stations to consumers so that they have access to a source of electricity
• Types of transformers used in the National Grid

  • Step-Up Transformers
  • Step-Down Transformers
• Where are step-up transformers found in the National Grid? What do they do?

  1. Step-Up Transformers are used when connecting power stations to transmission cables

  2. They increase the potential difference
• Where are step-down transformers found in the National Grid? What do they do?

  1. Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)

  2. They decrease the potential difference
• Why do transmission lines transfer electricity at high potentials?

  • A high potential, results in a low current
  • The lower the current, the less energy that is wasted as heat
  • Therefore it is more efficient
• Why does the potential need to be decreased between transmission lines and houses?

  • Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
  • Appliances are designed for 230V