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
Copper loss also referred to as "I squared R losses", in reference to Joule's First Law. This states that the energy lost each second, or power, increases as the square of the current through the windings and in proportion to the electrical resistance of the conductors. where I is the current flowing in the conductor and R the resistance of the conductor. With I in amperes and R in ohms, the calculated power loss is given in watts. Joule heating has a coefficient of performance of 1.0, meaning that every 1 watt of electrical power is converted to 1 Joule of heat.