Circuit Lab: Ohm's Law

How to use it

1. Choose series (one path) or parallel (two paths).
2. Change the battery voltage and the two resistors, R1 and R2.
3. Watch the bulbs: brightness follows the power each one uses. The moving dots show conventional current; faster dots mean more current.
4. Read the meters below the circuit for total resistance, current, the voltage across each bulb and total power.

Try this

1. In series with R1 = R2 = 10 Ω and 9 V, predict the current before you look. Then check.
2. Switch to parallel without changing anything else. Does the total current go up or down? Why?
3. In series, make R2 much larger than R1. Which bulb is brighter, and why?
4. In parallel, which branch carries more current: the one with the larger or the smaller resistor?

The science

Ohm's law: V = I × R. Power used by a resistor: P = V × I.

In series, resistances add (R = R1 + R2), the same current flows through both, and the battery voltage is shared in proportion to resistance.

In parallel, 1/R = 1/R1 + 1/R2, so the total resistance is smaller than either branch. Each branch gets the full battery voltage, and the currents add.

The model uses ideal wires and a battery with no internal resistance, and treats each bulb as a fixed resistor. Real bulbs change resistance as they heat up.