3.5.1.1
Potential Difference & Voltage
Current Electricity — AQA A-Level Physics
Key Definition
Potential difference — The work done per unit charge between two points in a circuit.
$$V = \frac{W}{Q}$$
- Where:
- $V$ = potential difference (V)
- $W$ = work done / energy transferred (J)
- $Q$ = charge (C)
- Potential differenceThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). (V) is measured in volts (V).
- 1 V = 1 J C⁻¹ (one joule of energyThe capacity to do work. Measured in joules (J). per coulombThe SI unit of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. One coulomb is the chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). transferred by a current of 1 A in 1 second. of charge).
- 1 V across a component means 1 J of energyThe capacity to do work. Measured in joules (J). is transferred per coulombThe SI unit of charge. One coulomb is the charge transferred by a current of 1 A in 1 second. passing through it.
- Potential differenceThe energy transferred per unit charge between two points. Measured in volts (V). is measured using a voltmeterAn instrument that measures potential differenceThe energy transferred per unit charge between two points. Measured in volts (V).. Connected in parallel across the component. Has very high resistanceThe opposition to currentThe rate of flow of charge. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of charge. Measured in amperes (A).. Measured in ohms (Ω)...
- A voltmeterAn instrument that measures potential difference. Connected in parallel across the component. Has very high resistance. must be connected in parallelComponents connected across the same two points, providing multiple current paths. with the component.
Examiner Tips and Tricks
- Use 'energy transferred per unit charge' in written answers.
- Examiners accept 'work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). per unit charge' as an equivalent.
Common Mistake
MEDIUM
Connecting a voltmeterAn instrument that measures potential difference. Connected in parallel across the component. Has very high resistance. in series instead of parallel. A voltmeterAn instrument that measures potential difference. Connected in parallel across the component. Has very high resistance. has very high resistanceThe opposition to currentThe rate of flow of charge. Measured in amperes (A). flow. The ratio of potential difference to current. Measured in ohms (Ω). and must be in parallel.