Energy Transfers

State two equations for the power of a circuit.

Power = Current x Potential differences 
Power = Current² x Resistance 

State an equation linking energy transferred, power and time.

Energy = Power x Time

State an equation linking energy transferred, charge flow and potential difference.

Energy = Charge (Coulombs) x Potential Difference (Volts)

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

• How long the appliance is being used for

• 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 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

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?

• Step-Up Transformers

• Step-Down Transformers

Where are step-up transformers found in the National Grid? 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? What do they do?

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

• 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