In an electrical circuit, the part that supplies voltage is typically the power source. The power source can be a battery, generator, or any other device that provides the potential difference (voltage) needed to push electric charges through the circuit. This potential difference is what drives the flow of electrons, creating an electric current.
For example, in a simple circuit powered by a battery, the battery supplies the voltage. The positive terminal of the battery has a higher potential energy than the negative terminal, creating a voltage difference between the two terminals. This voltage difference, measured in volts (V), is what motivates the movement of electrons through the circuit.
In more complex circuits, power sources like generators or power supplies provide the necessary voltage to drive various electrical components, such as resistors, capacitors, and inductors, which collectively perform different functions within the circuit.