Table of Contents
What Is Ohm's Law?
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance. Discovered by Georg Simon Ohm in 1827, it is the most fundamental relationship in electrical engineering and is used in virtually every circuit analysis.
Ohm's law applies to resistive (ohmic) materials where resistance remains constant regardless of voltage. Many real components are approximately ohmic within their normal operating range. Combined with Kirchhoff's laws, Ohm's law enables analysis of any linear circuit.
Formula
Where V is voltage in Volts, I is current in Amperes, and R is resistance in Ohms.
Ohm's Law Wheel (Power Combinations)
| Find | Using V & I | Using V & R | Using I & R |
|---|---|---|---|
| Power | P = VI | P = V²/R | P = I²R |
| Voltage | V = P/I | V = √(PR) | V = IR |
| Current | I = P/V | I = V/R | I = √(P/R) |
| Resistance | R = V/I | R = V²/P | R = P/I² |
Frequently Asked Questions
Does Ohm's law apply to AC circuits?
Yes, but resistance is replaced by impedance (Z) which includes resistance, capacitive reactance, and inductive reactance: V = IZ. For purely resistive AC circuits, Ohm's law applies directly using RMS values.
What materials don't follow Ohm's law?
Diodes, transistors, gas discharge tubes, and many semiconductors are non-ohmic. Their current-voltage relationship is nonlinear. For example, a diode follows an exponential I-V curve, and superconductors have zero resistance below their critical temperature.