Potential Difference (SQA National 5 Physics): Revision Note

Potential difference

• Potential difference, or voltage, is

A measure of the difference in energy per unit charge across two points in a circuit

• Voltage is measured in units of volts (V)

  • 1 volt is equivalent to the transfer of 1 joule of energy by 1 coulomb of charge, or 1 V = 1 J C^-1

• The potential difference between two points in a circuit is related to the amount of energy transferred between those points

• The potential difference, or voltage, of a supply is

A measure of the energy given to the charge carriers in a circuit

• This means that, as electrons pass through a cell, they gain energy

  • For example, in a 12 V cell, every coulomb of charge passing through gains 12 J of energy

• The potential difference, or voltage, across a component is

A measure of the energy given out by the charges as they pass through a component

• This means that, as electrons pass through a circuit, they lose energy

  • For example, after leaving the 12 V cell, each coulomb of charge will transfer 12 J of energy to the wires and components in the circuit

• The terminals of a cell make one end of the circuit positive and the other negative

  • This is the potential difference between two points that makes an electric current flow between them

Potential difference across a circuit