Energy Transfer

• What is one equation for the power of a circuit?

  P = I V
• What is another equation for the power of a circuit?

  P = I² R
• What are the units for power?

  Watts
• What are the units for current?

  Amperes
• What are the units for potential difference?

  Volts
• What are the units for resistance?

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

  E = P t
• What are the units for energy?

  Joules
• What are the units for time?

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

  E = Q V
• What are the units for charge?

  Coulombs
• What two main factors does the amount of energy transferred by an appliance depend on?

  Time used and power of appliance
• Describe the energy transfers in a battery powered torch.

  • Battery converts chemical energy to electrical energy
  • Bulb converts electrical energy to light and waste heat
• Describe the energy transfers in a battery powered motor.

  • Battery converts chemical energy to electrical energy
  • Motor converts electrical energy to kinetic energy and waste heat
• What three things determine the power of a circuit device?

  Potential difference, current, energy transferred
• What is the purpose of the National Grid?

  Link power stations to consumers
• What are the two types of transformers used in the National Grid?

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

  Connecting power stations to transmission cables
• What do step-up transformers do?

  Increase the potential difference
• Where are step-down transformers found in the National Grid?

  Connecting transmission cables to domestic buildings
• What do step-down transformers do?

  Decrease the potential difference
• Why do transmission lines transfer electricity at high potentials?

  To reduce current and energy loss
• Why does the potential need to be decreased between transmission lines and houses?

  Lower potentials are safer for domestic use
• What voltage are appliances designed for?

  230V