What is electrical voltage?
Electrical voltage: definition and unit
One of several electrical quantities
In an electrical circuit, we already encounter current, denoted by I and measured in amperes (A). Electrical voltage, denoted by U, is another essential quantity. It is measured between two points in a circuit, or between the two terminals of a dipole (battery, lamp, motor, etc.).
A simple definition
Electric voltage represents the difference in electric potential between two points. It can be thought of as the ‘force’ that drives electric charges to flow through the circuit, much like a difference in water level causes water to flow through a pipe.
Without voltage, there is no current: it is the voltage supplied by the generator (battery, mains supply, etc.) that sets the charges in motion.
Unit and symbol
Voltage is measured in volts, denoted by V, in honour of the Italian physicist Alessandro Volta. Derived units are also sometimes used:
| Unit | Symbol | Equivalence |
|---|---|---|
| kilovolt | kV | 1 kV = 1000 V |
| volt | V | base unit |
| millivolt | mV | 1 V = 1000 mV |
Practical example
- A standard flat battery delivers a voltage of 4.5 V.
- A round battery (AA or AAA) delivers 1.5 V.
- The mains supply (wall sockets) delivers approximately 230 V in France.
A common pitfall to avoid
Do not confuse voltage (U, in volts) and current (I, in amperes): these are two different quantities, which are not measured in the same way or with the same device connected in the same way to the circuit.