Voltage (U), Voltage, is the electrical force that sets electrons in motion, causing a current to flow. The unit of measurement for voltage is the volt (V), named after the Italian physicist Alessandro Volta (1743 to 1827), and is one of the basic quantities of the system of units( SI).
Voltage is characterized by its polarities, positive and negative. If the polarities of a voltage source remain unchanged, it is called DC voltage; if the polarities change, it is called AC voltage. A DC voltage causes a DC current in the circuit, an AC voltage causes an AC current. The higher the voltage, the higher the current it causes. A voltage of one volt drives one coulomb (`6.24 * 10^18`) of electrons, through a resistance of one ohm in one second.
The direction of voltage in electronic circuits is indicated by arrows. These always point from a higher to a lower potential, or from a positive voltage to a negative one. Typical DC voltage sources are batteries, accumulators and solar cells; a typical AC voltage source is the mains voltage.