Which rule expresses that the sum of voltages around a closed loop equals zero?

• A. KCL
• B. Ohm's law
• C. P = VI
• D. The sum of voltages around any closed loop equals zero

Answer: (D)

Kirchhoff's Voltage Law says the algebraic sum of all voltages around any closed loop is zero. This reflects conservation of energy: as you go around the loop, the energy supplied by sources is exactly balanced by the energy dropped across components, so the net change in voltage is zero. When you traverse the loop in a chosen direction and assign voltages as rises and drops, the numbers must add up to zero. The statement in the option matches this exactly, making it the best choice.

The other ideas describe different concepts: Kirchhoff's Current Law deals with how current splits and sums at a node, not voltages around a loop; Ohm's law relates voltage, current, and resistance for a component; P = VI connects power to voltage and current, again not the loop voltage balance. For a quick sanity check, if you go around a loop with a 12 V source and drops of 5 V and 7 V, the sum is +12 − 5 − 7 = 0, illustrating the rule in action.