Terminal voltage

Definition

Terminal voltage is the potential difference measured across the terminals of a battery or power supply when a current is flowing. It differs from the electromotive force (emf) due to the internal resistance of the power source.

5 Must Know Facts For Your Next Test

1. Terminal voltage is always less than the emf when a current is flowing due to internal resistance.
2. The formula for terminal voltage is $V_{terminal} = emf - Ir$, where $I$ is the current and $r$ is the internal resistance.
3. If no current flows, terminal voltage equals emf because there is no voltage drop across internal resistance.
4. Internal resistance causes energy loss within the battery, which affects terminal voltage.
5. Measuring terminal voltage requires placing a voltmeter across the terminals of the power source.

Review Questions

• How does terminal voltage differ from electromotive force (emf)?
• What happens to terminal voltage as internal resistance increases?
• How can you calculate terminal voltage if you know emf, current, and internal resistance?

Related terms

Electromotive Force (emf): The maximum potential difference between two electrodes of a battery when no current flows.

Internal Resistance:

Resistance within a battery or power supply that causes a drop in terminal voltage when current flows.

Ohm's Law:

$V = IR$, which relates voltage ($V$), current ($I$), and resistance ($R$) in an electrical circuit.