What is Ohm's Law?

• A. A fundamental principle used to calculate voltage, current, and resistance in electrical circuits.
• B. A law describing how power relates to energy and time.
• C. A rule about magnetic fields in circuits.
• D. A device for measuring impedance.

Answer: (A)

Ohm's Law describes the relationship between voltage, current, and resistance in a circuit. It is expressed as V = I R, so voltage equals current times resistance. This lets you calculate any one of the three if you know the other two. For example, with a 5-ohm resistor carrying 2 A, the voltage is 10 V. If you know voltage and resistance, current is I = V / R; if you know current and voltage, resistance is R = V / I. In AC circuits, you extend this to impedance with V = I Z, but for simple resistors the resistance stays constant. This principle is what you use to analyze and design circuits because it directly ties the measurable quantities together. Other choices describe power relationships, magnetic effects, or measuring devices, which are different concepts and don’t capture this direct V–I–R relationship.