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The graphic shows the potential rises and falls in a circuit with a battery providing a source of electromotive force (EMF) of magnitude

. The circuit contains a resistance

, as well as an internal resistance

. The associated changes in the potential add to

, when a current

passes through the points

(before the EMF source) and

(before the resistance) and back to

, with corresponding voltages

and

. These changes in the potential, when summed algebraically, must be equal to zero, by Kirchhoff's second rule.

The following conditions hold for the potential differences in the circuit:

and

For a detailed exposition, see D. Halliday, R. Resnick, and K. S. Krane, Physics, Vol. 2, 5th ed., New York: Wiley, 2001.

Contributed by: Enrique Zeleny

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Potential Differences in a Circuit with an EMF Source