Electromotive Force as Energy per Unit Charge

Steps:

• Define e.m.f. as the work done by a cell to separate charges, measured in volts (joules per coulomb).
• Recognize that e.m.f. quantifies chemical energy converted to electrical energy per unit charge in the cell.
• Compare options to the definition: e.m.f. = ε = W/Q, where W is chemical work done on charge Q.
• Select the option matching this energy transformation process.

Why D is correct:

• E.m.f. is defined as the chemical energy transformed into electrical energy per coulomb of charge passing through the cell, so 6V means 6J per coulomb (ε = W/Q).

Why the others are wrong:

• A: Describes energy loss in internal resistance, which reduces terminal voltage but is not e.m.f.
• B: Refers to terminal potential difference under load, not the open-circuit e.m.f.
• C: Implies charge gains energy externally, but e.m.f. specifically involves internal chemical transformation, not just any gain.

Final answer: D