Electric Potential and Potential Difference
Electric potential at a point is work done per unit charge to bring a test charge from infinity. Potential difference (voltage) is the difference in potential between two points.
Try the simulator
Electric potential
The electric potential at a point is the work done per unit charge in bringing a small positive test charge from infinity to that point without acceleration. It is a scalar. The SI unit is the volt (V): 1 V = 1 J/C. Potential is relative; we often take earth or the negative terminal of a battery as zero.
Potential difference (voltage)
The potential difference (p.d.) between two points A and B is the work done per unit charge in moving a charge from A to B. So V = W/Q, or V = E/Q. It is measured in volts. In a circuit, the battery provides a potential difference across its terminals; this drives the current through the circuit.
Why it matters in circuits
Current flows from higher potential to lower potential (in the direction of the field). Resistors have a potential drop V = IR. Understanding potential difference is essential for analysing series and parallel circuits and for power calculations.
If we take the negative terminal as zero potential, what does the battery voltage tell you about the positive terminal?