Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to move a positive test charge from the first point to the second point. In the International System of Units (SI), the derived unit for voltage is the volt (V). The voltage 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 a generator). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, photovoltaic effect, and the thermoelectric effect. Since voltage is the difference in electric potential, it is a physical scalar quantity. A voltmeter can be used to measure the voltage 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. In this case, voltage is often mentioned at a point without completely mentioning the other measurement point. A voltage can be associated with either a source of energy or the loss, dissipation, or storage of energy.
Definition The SI unit of work per unit charge is the joule 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 Josephson effect was used, and in 2019 physical constants were given defined values for the definition of all SI units. Voltage is denoted symbolically by Δ V {\displaystyle \Delta V} , simplified V, especially in English-speaking countries. Internationally, the symbol U is standardized. The electrochemical potential is the voltage that can be directly measured with a voltmeter. The Galvani potential that exists in structures with junctions of dissimilar materials, is also work per charge but cannot be measured with a voltmeter in the external circuit (see § Galvani potential vs. electrochemical potential). Voltage is defined so that negatively charged objects are pulled towards higher voltages, while positively charged objects are pulled towards lower voltages. Therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Historically, voltage has been referred to using terms like "tension" and "pressure". Even today, the term "tension" is still used, for example within the phrase "high tension" (HT) which is commonly used in the contexts of automotive electronics and systems using thermionic valves (vacuum tubes).
Electrostatics
In electrostatics, the voltage increase from point r A {\displaystyle \mathbf {r} _{A}} to some point r B {\displaystyle \mathbf {r} _{B}} is given by the change in electrostatic potential V {\textstyle V} from r A {\displaystyle \mathbf {r} _{A}} to r B {\displaystyle \mathbf {r} _{B}} . By definition, this is:
… excerpt ends here. Continue reading the full article.
