Complete Guide to Ohm's Law
The Ohm's Law Calculator instantly computes voltage, current, resistance, or power using V = IR and P = VI. Essential for students, electricians, and engineers. Our free tool supports all combinations with clear formulas.
What is Ohm's Law?
V = I × R: Voltage equals current times resistance. Discovered by Georg Ohm in 1827. Applies to linear conductors at constant temperature.
Related: P = V × I, R = V / I, I = V / R.
Why Use Ohm's Law?
Critical for:
- Circuit Design: Size components.
- Troubleshooting: Diagnose faults.
- Safety: Prevent overloads.
- Education: Learn fundamentals.
Pair with Voltage Drop and Power Factor.
Ohm's Law Formulas
| Known | Find | Formula |
|---|---|---|
| V, I | R | R = V / I |
| V, R | I | I = V / R |
| I, R | V | V = I × R |
| P, V | I | I = P / V |
| P, I | V | V = P / I |
| P, R | I | I = √(P / R) |
Power Triangle
P (Watts) = V (Volts) × I (Amps). For DC and resistive AC loads.
Example: 12V, 2A → R = 6Ω, P = 24W.
Units & Prefixes
| Unit | Symbol | Prefix | Value |
|---|---|---|---|
| Volt | V | kV | 1000 V |
| Amp | A | mA | 0.001 A |
| Ohm | Ω | MΩ | 1,000,000 Ω |
| Watt | W | kW | 1000 W |
Practical Examples
- LED Resistor: 5V, 20mA → R = 150Ω.
- Heater: 240V, 1500W → I = 6.25A.
- Battery: 12V, 50Ω → I = 0.24A.
- Motor: 10A, 8Ω → V = 80V.
Limitations of Ohm's Law
- Not for non-linear devices (diodes, transistors).
- Temperature affects resistance.
- High frequency: skin effect.
- AC: use impedance (Z = R + jX).
Ohm's Law Wheel
Visual aid: Center = P, quadrants = V, I, R. Formulas around the wheel.
Common Mistakes
- Forgetting units (mA vs A).
- Using AC formulas for DC.
- Ignoring temperature coefficient.
- Mixing power and energy (W vs Wh).
Advanced Applications
- Kirchhoff's Laws: Combine with Ohm's.
- Thevenin Equivalent: Simplify circuits.
- Maximum Power Transfer: R_load = R_source.
- Superposition: Analyze multi-source.
Conclusion
Ohm's Law is the foundation of electrical engineering. Our Ohm's Law Calculator provides instant, accurate results for any two known values. Master circuits with 1000 Calculators.