2.4

• What are the two equations for the power of a circuit?

  P = I V and P = I² R
• What are the appropriate units for power, current, potential difference, and resistance?

  Power (Watts), Current (Amperes), Potential Difference (Volts), Resistance (Ohms)
• What is the equation linking energy transferred, power, and time?

  E = P t
• What are the appropriate units for energy, power, and time?

  Energy (Joules), Power (Watts), Time (Seconds)
• What is the equation linking energy transferred, charge flow, and potential difference?

  E = Q V
• What are the appropriate units for energy, charge, and potential difference?

  Energy (Joules), Charge (Coulombs), Potential Difference (Volts)
• What two main factors does the amount of energy transferred by an appliance depend on?

  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 and waste energy (heating)
• Describe the energy transfers in a battery powered motor.

  • Battery converts chemical energy into electrical energy
  • Motor converts electrical energy into kinetic energy and waste energy (heating due to friction)
• What three things 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 for access to 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 and 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 and they decrease the potential difference.
• Why do transmission lines transfer electricity at high potentials?

  A high potential results in a low current, reducing energy wasted as heat and increasing efficiency.
• Why does the potential need to be decreased between transmission lines and houses?

  Lower potentials are safer for domestic use and reduce the likelihood of severe electrocution; appliances are designed for 230V.