Voltage power and current, where 1 volt = 1 watt (of power) per 1 ampere (of current). This definition is equivalent to the more commonly used 'joules per coulomb'. Voltage or electric potential difference is denoted symbolically by , but more often simply as "V", for instance in the context of Ohm's or Kirchhoff's circuit laws. Electric potential differences between points can be caused by electric charge, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage (or potential difference) between two points in a
Ampere-turn been used in industry, specifically, US-based coil-making industries. In Thomas Edison's laboratory Francis Upton was the lead mathematician. Trained with Helmholtz in Germany, he used "weber" as the name of the unit of current, modified to "ampere" later: Ampere-turn The ampere-turn (At) is the MKS (Metres, Kilograms, Seconds) unit of magnetomotive force (MMF), represented by a direct current of one ampere flowing in a single-turn loop in a vacuum. "Turns" refers to the winding number of an electrical conductor composing an inductor. For example, a current of 2 A flowing through a coil of 10 turns produces an MMF of