Electromotive Force as Work per Unit Charge

Steps:

• Recall that emf is defined as the energy provided by a source per unit charge moved.
• Express this as emf = work done (or energy) / charge.
• Examine options: A and C involve time, relating to power; B uses "work done," but D simplifies to "work."
• Match D directly to the formula ε = W / q, confirming it as the emf expression.

Why D is correct:

• Emf is defined by the formula ε = W / q, where W is work done by the battery and q is charge, representing potential difference in volts.

Why the others are wrong:

• A: Work done / time equals power (P = W / t), not emf.
• B: "Work done / charge" is conceptually similar but uses redundant phrasing; D is the standard concise form.
• C: Work / time also equals power, unrelated to emf.

Final answer: D