Energy Transfers

• What is the first equation for calculating the power of a circuit?

  $P = I V$
• What is the second equation for calculating the power of a circuit?

  $P = I^2 R$
• What is the unit for power?

  Watts
• What is the unit for current?

  Amperes
• What is the unit for potential difference?

  Volts
• What is the unit for resistance?

  Ohms
• What is the equation linking energy transferred, power, and time?

  $E = P t$
• What is the unit for energy?

  Joules
• What is the unit for power in the energy equation?

  Watts
• What is the unit for time in the energy equation?

  Seconds
• What is the equation linking energy transferred, charge flow, and potential difference?

  $E = Q V$
• What is the unit for charge?

  Coulombs
• What is the unit for potential difference in the energy equation?

  Volts
• On what two factors does the amount of energy transferred by an appliance depend?

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

  • Battery converts chemical energy into electrical energy
  • 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.

  • Battery converts chemical energy into electrical energy
  • Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
• What three factors determine the power of a circuit device?

  1. The potential difference across the circuit
  2. The current through the circuit
  3. The amount of energy transferred in a given time
• What is the purpose of the National Grid?

  To link power stations to consumers so that they have access to a source of electricity.
• What are the two types of transformers used in the National Grid?

  1. Step-Up Transformers
  2. Step-Down Transformers
• Where are step-up transformers found in the National Grid and what do they do?

  • Step-Up Transformers are used when connecting power stations to transmission cables
  • They increase the potential difference
• Where are step-down transformers found in the National Grid and what do they do?

  • Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)
  • They decrease the potential difference