Faraday had shown that electromotive force depends on chemical affinity.
The quantity ½Ir2w is the electromotive force due to the disk.
Helmholtz takes the case of a circuit of resistance R in which acts an electromotive force due to a battery or thermopile.
The electromotive force of one cell of a Daniell battery is about one volt.
The electromotive force of this secondary current is somewhat higher than is necessary.
The electromotive force of this cell when new is about 1.47 volts.
The practical electrician has to measure electrical resistance, electromotive forces, and the capacities of condensers.
The electromotive power of this element may be as high as 1.8 D.
Its electromotive force is nearly two volts, but it has the objection of giving off disagreeable nitrous fumes.
What may be said of the electromotive force during the second half of the revolution?