How it’s calculated
Ohm's law relates the voltage across an ohmic conductor to the current through it and its resistance. Rearrange it to find whichever quantity is unknown; power follows from P = VI.
Example: a 12 V source across a 6 Ω resistor drives I = 12 ÷ 6 = 2 A, dissipating P = 12 × 2 = 24 W.
Ohm's law holds for resistors and most metal conductors at constant temperature. Diodes, lamps with hot filaments and other non-ohmic devices do not follow it exactly.
Frequently asked questions
What is Ohm's law?
Voltage equals current times resistance (V = IR). One volt drives one ampere through one ohm.
Does Ohm's law work for AC circuits?
For purely resistive AC loads, yes, using RMS voltage and current. With motors, capacitors or inductors you need impedance instead of resistance.
Why does the calculator also show power?
Power tells you how much heat a resistor must dissipate. Pick a resistor rated comfortably above it, typically at least double.
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Sources
- University Physics Volume 2, §9.4 Ohm's Law — OpenStax
- University Physics Volume 2, §9.5 Electrical Energy and Power — OpenStax
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
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