Electromotive Force as Work per Unit Charge

Steps:

• Identify the quantity: work (joules) divided by charge (coulombs) gives joules/coulomb, equivalent to volts.
• Recognize this as potential difference, specifically the work done by a source to move unit charge around a complete circuit.
• Recall that in circuits, this measures the energy provided by the power source per unit charge.
• Match to definition: this exactly describes electromotive force (EMF).

Why D is correct:

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

Why the others are wrong:

• A: Electric current is charge flow per unit time (I = Q/t, in amperes).
• B: Electric resistance opposes current flow (R = V/I, in ohms).
• C: Electrical power is energy transfer rate (P = VI, in watts).

Final answer: D