Electromotive Force as Work per Unit Charge

Steps:

• Identify the definition: electrical work by a source to move unit charge around a complete circuit.
• Recall key electrical terms: power (rate of energy transfer), potential difference (voltage drop across points), electromotive force (source-driven work per charge), energy (total work capacity).
• Match definition to electromotive force, which specifies source work in a closed loop.
• Eliminate mismatches: power and energy lack per-unit-charge aspect; potential difference ignores full-circuit source role.

Why C is correct:

• Electromotive force (EMF) is defined as ε = W/Q, the work W done by the source per unit charge Q in a complete circuit.

Why the others are wrong:

• A: Power is work per unit time (P = W/t), not per unit charge.
• B: Potential difference is work per unit charge between two points (V = W/Q), not full-circuit source work.
• D: Energy is total work done (W), not normalized per unit charge.

Final answer: C