Electromotive force (emf, ) is a term use to characterize electrical devices, such as voltaic cells, thermoelectric devices, electrical generators and transformers, and even resistors. For a given device, if a charge Q passes through that device, and gains an energy U, the net emf for that device is the energy gained per unit charge, or U/Q. This has units of volts, or newton meters per coulomb, and hence can be thought of as a voltage induced by the device in question. Since force has the unit of the newton, emf is a misnomer, but one that over time has resisted change.