Which law is used to relate voltage drop, current, and resistance in conductor calculations?

• A. Watt's Law
• B. Kirchhoff's Law
• C. Ohm's Law
• D. Newton's Law

Answer: (C)

Ohm's Law describes how voltage drop, current, and resistance relate in a conductor. It states that the voltage drop across a conductor equals the current through it times its resistance, V = I × R. This means that for a given resistance, the voltage drop scales with current, and for a given voltage, the current is determined by the resistance (I = V/R). It’s the fundamental tool for predicting how much voltage will be lost along a wire or component when a certain current flows, or for sizing conductors to keep drops within acceptable limits. For example, if a wire has 2 ohms of resistance and 3 amperes pass through it, the voltage drop is 6 volts. If the current doubles while resistance stays the same, the drop doubles as well. Other listed ideas touch on related topics—Watt's Law connects power to voltage and current (and can be rewritten using Ohm's Law), Kirchhoff's Law deals with the sum of currents or voltages in a circuit, and Newton's Law governs mechanics, not electrical relationships.