ELECTROMOTIVE FORCE
The pressure that causes current to flow is called electromotive force (EMF). EMF is measured in “volts,” whose symbol is V (named after Alessandro Volta). Since we need to determine (by using the volt) how much “potential” energy there is in a difference of charge, two of the terms already introduced will suffice. The joule is a basic unit of energy, the coulomb is the basic unit of charge, and since the electrical pressure is the energy in a difference of charge, it may be stated arithmetically as:
V (volts) = energy (in joules)/charge (in coulombs)
Or in words as:
a 10-volt battery means that each coulomb of charge provides 10 joules of energy (or work). By rearranging the relationship to show work (or energy), it becomes:
WORK = VOLTS × CHARGE
