Ohm’s Law Circuit Lab

Voltage pushes. Resistance opposes. Current is what actually flows. One short equation ties all three together, and this simulation lets you see it rather than just read it.

Ohm's Law Circuit

Voltage, current and resistance in one loop

Ohm’s law

I = V / R

Current (in amperes) equals voltage (in volts) divided by resistance (in ohms). Double the voltage and you double the current. Double the resistance and you halve it. That is the whole law.

The I–V graph under the circuit shows why it is called a law and not just a formula: for a fixed resistance, plotting current against voltage gives a perfectly straight line through the origin, and the slope of that line is 1/R.

Power: what the circuit actually does

Current alone does not tell you how much work the circuit performs. For that you need power:

P = V × I = V² / R

Power is measured in watts, and it is what the lamp in the simulation responds to. Drop the resistance to 5 Ω and the lamp blazes; push it to 90 Ω and it barely glows, even though the battery voltage never changed.

Note the V² term. Because power scales with the square of voltage, doubling the voltage does not double the brightness — it quadruples the power. This is why electrical transmission uses very high voltages: for the same delivered power, higher voltage means lower current, and lower current means far less energy wasted as heat in the wires.

Try this

Set R = 20 Ω. Now read the current at 6 V, then at 12 V, then at 24 V. It should double each time.
Press “Low R — bright” and watch both the current and the lamp. Then press “High R — dim”.
Watch the orange dot on the I–V graph. It always sits exactly on the blue line, no matter how you move the sliders.

Why it matters