Volt equals power per unit current

Steps:

• Recall the power formula: electrical power P in watts equals voltage V times current I in amperes, so P = V × I.
• Rearrange the formula to solve for voltage: V = P / I.
• Substitute units: P is in watts and I is in amperes, so V is in watts per ampere.
• Confirm that this unit combination matches the definition of the volt as the potential difference driving one ampere through one ohm.

Why D is correct:

• From the power formula P = V I, rearranging gives V = P / I, so the unit volt equals watt / ampere.

Why the others are wrong:

• A. ampere/ohm equals volt/ohm², which is resistance per unit voltage.
• B. ampere/watt equals 1/volt, the reciprocal of voltage.
• C. ohm/ampere equals volt/ampere², which is voltage per unit current squared.

Final answer: D