phy~old Q

係out syl架啦
如果見到呢個字
你當佢係voltage

Electromotive force or potential of a body is the work done in joules to bring a unit electric charge from infinity to the body
Electromotive force (emf, ) is a term used 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 across 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 (V), or newton-meter/coulomb (N-m/C), and hence can be thought of as a voltage induced by the device in question. Since force has the unit of newton (N), emf is a misnomer, but one that over time has resisted change.

In most circuits current is driven by a so-called "source of emf", which usually is a voltaic cell (or battery, which consists of voltaic cells in series and/or in parallel) or the power company. For a voltaic cell the source of emf is the chemical reactions that occur at each of the electrode-electrolyte interfaces, so that a voltaic cell can be thought of as two "surface pumps" of atomic dimension. The reactions at the electrode-electrolyte interfaces provide the "seat" of emf for the voltaic cell. For the power company, the source of emf is electromagnetic induction, which is more extended than an atomic size, but nevertheless is confined to the power generation building, usually many miles from the user.