The term survives from the time when electric current and electrical energy were not clearly understood. An emf is a potential difference, not a force.

The term emf is used to represent the open circuit voltage of a battery or power supply. (That is, the measured potential difference between the terminals when no current is drawn, and there is no voltage drop across the internal resistance).

The symbol E is used for emf to distinguish it from the measured voltage V when current is drawn.

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