Voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension is the difference in electric potential between two points.[1][2] 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). [3][4][5]
For other uses, see Voltage (disambiguation).
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).[6][7] 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. Since it is the difference in electric potential, it is a physical scalar quantity.[8]
A voltmeter can be used to measure the voltage between two points in a system.[9] Often a common reference potential such as the ground of the system is used as one of the points. A voltage can be associated with either a source of energy or the loss, dissipation, or storage of energy.
History[edit]
The term electromotive force was first used by Volta in a letter to Giovanni Aldini in 1798, and first appeared in a published paper in 1801 in Annales de chimie et de physique.[25]: 408 Volta meant by this a force that was not an electrostatic force, specifically, an electrochemical force.[25]: 405 The term was taken up by Michael Faraday in connection with electromagnetic induction in the 1820s. However, a clear definition of voltage and method of measuring it had not been developed at this time.[26]: 554 Volta distinguished electromotive force (emf) from tension (potential difference): the observed potential difference at the terminals of an electrochemical cell when it was open circuit must exactly balance the emf of the cell so that no current flowed.[25]: 405