Potential Difference as Energy per Unit Charge

Steps:

• Recall that potential difference (p.d.) measures the work done to move a unit charge between two points.
• Express this as p.d. = energy transferred / charge, or V = W / Q.
• Compare to options: A matches energy per unit charge directly.
• Eliminate mismatches: B, C, D involve power or current, not the core definition.

Why A is correct:

• By definition, p.d. is the energy transferred per unit charge, as in the formula V = W / Q, where V is volts, W is joules, and Q is coulombs.

Why the others are wrong:

• B: Power per unit current equals resistance (P = I²R), not p.d.
• C: Energy per unit current lacks charge basis; it's not a standard definition.
• D: Power per unit charge relates to electric field strength, not p.d.

Final answer: A