Electromotive force

Definition

Electromotive force (emf) is the energy provided by a source per unit charge to move electrons through a circuit. It is measured in volts (V) and drives the current around the circuit.

5 Must Know Facts For Your Next Test

1. Electromotive force (emf) is not actually a force but rather a potential difference.
2. The symbol for electromotive force is usually $\varepsilon$.
3. Emf is generated by various sources like batteries, solar cells, and generators.
4. The terminal voltage of a power source is less than its emf due to internal resistance.
5. Emf can be calculated using the formula $\varepsilon = V + Ir$, where $V$ is the terminal voltage, $I$ is the current, and $r$ is the internal resistance.

Review Questions

• What does electromotive force (emf) measure in a circuit?
• How does internal resistance affect the terminal voltage compared to emf?
• Write down and explain the formula relating emf, terminal voltage, current, and internal resistance.

Related terms

Terminal Voltage: The voltage output of a device measured across its terminals when it is delivering current.

Internal Resistance: The inherent resistance within an electrical source that causes a drop in the output voltage when there is a current.

Current: The flow of electric charge through a conductor between two points having a difference in potential.