alleryStart learning →What exactly is the electromotive force of a voltage source?
AThe force it exerts on each unit of charge
BThe current it drives through a short circuit
CIts potential difference when no current flows
DIts potential difference under its rated load
Answer & Solution
Correct answer: C. Its potential difference when no current flows
1. Despite its name, emf is not a force at all but a special kind of potential difference, measured in volts.
2. It is the potential difference across the terminals when no current is being drawn.
3. Once current flows, the internal resistance takes a share and the terminal reading falls below the emf.
4. The reading under a rated load is therefore terminal voltage, not emf.
_Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.2 Electromotive Force: Terminal Voltage_
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