POTENTIAL OR ELECTRO-MOTIVE FORCE.
This (commonly E. M. F.) is the term used for electrical energy or power of doing work, and is used in the same manner as “pressure” is applied to steam; in other words, it is the term used to express the force which tends to move electricity from one place to another, and is proportional to the difference of potential at the two places.
The earth’s surface is called “Zero Potential,” and is a reference point to measure the relative condition of other bodies. A positively electrified body is said to have a higher potential than the earth, which in turn has a higher potential than a negatively electrified body.
When two dissimilar metals touch each other, there is a difference of potential at point of contact. If zinc is in contact with copper it is of higher potential. In a series of disks of copper, zinc and wet cloths, arranged one over the other in above order, the wet cloth is the conductor, and current will flow on joining last copper and zinc by wire, etc.
This arrangement is called a voltaic pile (after its inventor, Volta), and the difference of potential produced is proportionate to the number of pairs of disks.
A difference of potential between two points connected will cause current to flow till the potentials of both points are the same.