Emf

Definition

Electromotive force (emf) is the energy provided per unit charge by an energy source, such as a battery or generator. It is measured in volts and represents the potential difference that drives current around a circuit.

5 Must Know Facts For Your Next Test

1. Emf is not a force but a potential difference measured in volts.
2. In a closed loop, the sum of emf sources equals the sum of voltage drops according to Kirchhoff’s Voltage Law.
3. Emf sources can be both ideal and real; real sources have internal resistance.
4. The symbol for emf in equations is usually $\mathcal{E}$ or $E$.
5. A higher emf means more energy per charge is available to do work in the circuit.

Review Questions

• What does electromotive force (emf) measure and in what units?
• How does Kirchhoff’s Voltage Law relate to emf in a closed loop?
• What is the significance of internal resistance in real emf sources?

Related terms

Voltage:

The electrical potential difference between two points, measured in volts.

Internal Resistance:

The resistance within an electrical source that causes a drop in the source voltage when there is a current.

Kirchhoff's Voltage Law:

$KVL$ states that the sum of all electric potential differences around any closed network is zero.