Which law of electricity is the most important?

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

Answer: (B)

Ohm's Law is the essential relationship in basic circuit work: voltage equals current times resistance (V = I × R). This simple formula ties together the three quantities you most often deal with, so knowing any two lets you find the third. It also connects to power, since P = V × I, meaning you can determine how much heat a component will dissipate and design safely accordingly. In practical maintenance and troubleshooting, this lets you quickly calculate how much current will flow through a resistor for a given supply, or what voltage is needed to achieve a desired current, or how to find an unknown resistance from measured voltage and current.

While the other laws have important roles—Ampere's Law describes magnetic fields around currents, Kirchhoff's Laws help analyze multi-loop circuits by enforcing conservation of current and energy, and Faraday's Law governs induction from changing magnetic fields—they’re more specialized. Ohm's Law provides the direct, universally applicable tool for everyday circuit analysis, which is why it’s considered the most important.