Temperature > 20 - Electromotive Force

Electromotive force (EMF), usually denoted as , is the property of any device which tends to cause the production of electric current in a circuit. It is a scalar quantity and should not be confused with an electric potential difference (EPD), although both have the same unit of measurement. In the International System of Units the unit of electromotive force and EDP is J/C (Joule per Coulomb), better known as V (volt). The EDP between two points is the work per unit charge that the electrostatic force does on a charge that is transported from one point to another; the EDP between two points is independent of the path or path that connects one point to the other. The electromotive force is the work per unit charge that a non-electrostatic force does when a charge is transported from one point to another along a particular path; that is, the electromotive force, unlike the EDP, depends on the path. For example, the electromotive force in a cell or battery only exists between two points connected by a path internal to these sources.

All materials exert some resistance, however small, to the flow of electrons, which causes an unwanted loss of energy (Joule effect). It is no different with generators, that is, as the current passes from the negative to the positive pole, there is a loss of energy due to the internal resistance of the device itself.

Therefore, the energy that will reach the resistor connected to the generator will not be total, since the DDP between the generator terminals and the resistor terminals will be different. To calculate what the DDP of the resistor terminals will be, we use the so-called Generator Equation, which, mathematically, translates into the form V = Є – ri.

It is worth remembering that there are no generators whose electromotive force is equal to the resistor's DDP, since any and all materials exert resistance. However, for calculation purposes, it is quite common to use the expression ideal generator, which would be nothing more than one whose internal resistance is zero, that is, there would be no unwanted losses in the circuit's power.