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Ohm's Law

What decides how much current flows?

Try it

Change the voltage. Then change the resistance.

Interactive circuit

6.0 Ω6.0 V
6.0 V
6.0 Ω

Voltage

6.0V

Resistance

6.0Ω

Current

1.00A

What changed

Move either slider and watch the current. Voltage and resistance pull it in opposite directions.

See the relationship

Current rises in a straight line with voltage. Raising the resistance tilts that line down — same voltage, less current.

Current against voltageVoltage on the horizontal axis from 0 to 12 volts. Current on the vertical axis from 0 to 12 amps. The curve falls steeply and then flattens, so current drops as voltage rises. Current state: voltage 6 volts, current 1 amps.R = 6.0 Ω

Current1 A · 6 V

Why does this happen?

Voltage is the push that drives charge around the circuit, and resistance is what opposes it. Push harder and more charge flows each second. Add resistance and less gets through.

Ohm's Law

For a fixed resistance, the current through a conductor is directly proportional to the voltage across it, and inversely proportional to its resistance.

Formula

V = I × R

V = voltage · I = current · R = resistance

Find current

I = V / R

Find resistance

R = V / I

Let's try one

A 12 V battery is connected across a 4 Ω resistor.

What current flows?