Voltage

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt.[1]:166 In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The old SI definition for volt used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units.[1]:177f,197f Voltage or electric potential difference is denoted symbolically by ${\displaystyle \Delta V}$, simplified V,[2] especially in English-speaking countries or international U,[3] for instance in the context of Ohm's or Kirchhoff's circuit laws.

Voltage
Batteries are sources of voltage in many electric circuits.
Common symbols
V , V , U , U
SI unitvolt
In SI base unitskg⋅m2⋅s−3⋅A−1
Derivations from
other quantities
Voltage = Energy / charge
DimensionM L2 T−3 I−1

Electric potential differences between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in generator, inductors, and transformers).[4][5] On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, and the thermoelectric effect.

A voltmeter can be used to measure the voltage (or potential difference) between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. A voltage can represent either a source of energy or the loss, dissipation, or storage of energy.