Which law is concerned with the sum of voltages around a closed loop?

• A. Kirchhoff's Voltage Law.
• B. Ohm's Law.
• C. Faraday's Law.
• D. Ampere's Law.

Answer: (A)

Around a closed circuit loop, the total voltage change must equal zero. This comes from energy conservation: as you move through sources and elements, the energy provided by sources is exactly used up by drops across components, so you return to the same electric potential you started with.

In practice, you traverse the loop and add up voltage rises and drops, using a consistent sign convention. A voltage rise is added, a voltage drop is subtracted, and the sum around the loop is zero. For example, with a single battery and a resistor carrying current, moving from the negative to the positive terminal gives a rise of E, and passing through the resistor drops IR; summing around the loop gives E − IR = 0, which yields E = IR. This idea generalizes to loops with many sources and elements.

Other laws in the list describe different ideas: Ohm's Law relates voltage, current, and resistance at a single element; Faraday's Law deals with induced emf from changing magnetic flux; Ampere's Law relates magnetic fields to currents.