Electromotive force is best described as what?

• A. The energy per unit charge delivered to move charges around a circuit
• B. The current times resistance
• C. The magnetic flux
• D. The potential difference across a component is EMF

Answer: (A)

EMF is the energy per unit charge that a source provides to push charges around a closed circuit. It represents the work done on each coulomb of charge by the battery or generator as it drives current, supplying energy that can be converted to light, heat, motion, and so on. That’s why it’s measured in volts. It isn’t the current times resistance (that quantity is power-related, or the voltage drop across a resistor), and it isn’t magnetic flux (which is a measure of the magnetic field linked with the loop). Nor is the potential difference across a single component equal to EMF; the latter is the energy per unit charge supplied by the source to move charges around the entire loop, while a component’s potential difference is the energy change per unit charge as charges move between two points in the circuit.