Electric power
lastmod 2025-11-05created 2025-11-051 edits
Electric power generally refers to the ability of electrical energy to do work; its operational definition is the amount of work done per unit time by electric current, or by electrical energy transferred or converted per unit time. It can be used to express the power consumption capacity of electrical equipment (a physical quantity indicating how fast it consumes electrical energy), the generating capacity of power generation facilities, the transmission capacity of transmission and transformation facilities, and so on. Power is denoted by P, and its unit is the watt (Watt), denoted by W.
Definition
In an electric circuit, power is defined by the relationship between current and electrical resistance. In a simple electric circuit like the one in the figure, the electrical resistance R generates heat while consuming current.
In 1840, the British physicist James Prescott Joule discovered that the amount of heat generated by a resistance in an electric circuit follows the relationship below. This is called Joule's law.
\({\displaystyle Q=I^{2}Rt}\)
- Q: amount of heat [J]
- I: current intensity [A]
- R: electrical resistance of the conductor [Ω]
- t: time the current flows [s]
Heat is generated in the resistance of an electric circuit because electrons passing through the resistance lose electric potential energy as they collide with the atoms in the resistance. The energy lost by the electrons is converted into vibrational energy of the atoms in the resistance, and as a result heat is generated. The heat generated this way is called Joule heating, and such conversion is called \({\displaystyle I^{2}R}\) loss. Power can be described as the amount of Joule heat generated per unit time consumed by the entire electric circuit.
Meanwhile, since voltage can be expressed as the product of current and resistance, the equation above can be simplified as follows.
\({\displaystyle P=VI}\)
- P: Korean: 전력 (Korean: 와트, W, Watt)
- V: Korean: 전압 (Korean: 볼트, V, Volt)
- I: Korean: 전류 (Korean: 암페어, A, Ampere)
Therefore, power can be expressed as the product of voltage and current.