Ohm's Law, Explained Simply
Updated 2026-07-12
Ohm's law relates the three basic quantities in an electric circuit: voltage equals current times resistance, written V = I R. Rearranged, current is voltage divided by resistance, and resistance is voltage divided by current.
Ohm's law is one equation with three faces. Voltage is the push, current is the flow, and resistance is how much the circuit fights the flow. Know two of them and the third follows.
The three quantities
Voltage (V, in volts) is the electrical push. Current (I, in amps) is the rate of charge flow. Resistance (R, in ohms) opposes that flow. Ohm's law ties them together as V = I R.
Rearranging safely
To find current, divide voltage by resistance: I = V / R. To find resistance, divide voltage by current: R = V / I. A quick sanity check: more resistance for the same voltage means less current.
Worked example
A 12 volt battery is connected across a 4 ohm resistor. What is the current?
- Start from Ohm's law: V = I R.
- Solve for current: I = V / R.
- Substitute: I = 12 / 4.
Answer: I = 3 amps.
The common mistake
Wrong: Multiplying voltage by resistance to get current.
Fix: Current is voltage divided by resistance, I = V / R. Multiplying would give the wrong units and a wrong answer. Higher resistance should lower the current, not raise it.
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Frequently asked questions
What is Ohm's law?
It states that voltage equals current times resistance, V = I R. It links the push (voltage), the flow (current), and the opposition to flow (resistance) in a circuit.
How do you find current using Ohm's law?
Divide the voltage by the resistance: I = V / R. For example, 12 volts across 4 ohms gives 3 amps.