功率作为电阻的函数
The power dissipated by a resistor may be calculated from its resistance, and the voltage or current involved. The formula is a combination of Ohm's law and Joule's law where: P = V ∙ I = V²⁄R = I² ∙ R. Where:
P是幂
R是电阻
是电阻两端的电压
是通过电阻器的电流
A linear resistor has a constant resistance value over all applied voltages or currents. Many practical resistors are linear over a useful range of currents. Non-linear resistors have a value that may vary depending on the applied voltage (or current). Where alternating current is applied to the circuit (or where the resistance value is a function of time), the relation above is true at any instant but calculation of average power over an interval of time requires integration of instantaneous power over that interval.
由于欧姆属于相关的单位系统，当这些量中的每一个都有其对应的SI单位（P代表瓦特，R代表欧姆，V代表伏特，I代表安培时，这个公式在数值上仍然有效当这些单位被使用时（并被认为被取消或省略）。