A series and parallel circuit simulator with two meters on it
Mokxi is a free online series and parallel circuit simulator that runs in your browser, with nothing to install and no account needed. A 9 V battery, a 1 k resistor in series, and a 2.2 k and a 4.7 k in parallel after it, on a real breadboard. One meter reads the current out of the battery, the other the voltage across the parallel pair, so both rules are on screen at once.
- 455parts on the bench
- 43boards running now
- 1.00xreal time, on every board
What you can do here
In the circuit above, or in the editor it opens.
- Read the total current and the voltage across a parallel pair at once
- Move the amps meter into one branch and read that branch alone
- Delete a resistor and watch the current and the voltages move
- Swap the 9 V battery for AA cells or an 18650, or run it down
- Check Kirchhoff’s laws: the currents into a node add up, the voltages around a loop add up
- Build any resistor network and measure it on the ohms range
What the running circuit shows
One current through the series part, one voltage across the parallel part.
The 2.2 k and the 4.7 k sit between the same two columns of the breadboard, which is what parallel means: one voltage across both. Together they are 2.2 k × 4.7 k / (2.2 k + 4.7 k) = 1.50 k, always less than the smaller of the two, so the whole string is 2.50 k. In the engine the battery gives about 3.84 mA and the pair has about 5.75 V across it.
The 1 k in series carries all of that current, so it drops 3.84 V, and 3.84 V plus 5.75 V is the 9.59 V on the battery’s terminals. In the pair the current splits the other way from the resistance: about 2.61 mA through the 2.2 k and 1.22 mA through the 4.7 k, which add back up to 3.84 mA. Those two sums are Kirchhoff’s voltage and current laws, read off a meter.
Delete the 4.7 k and the current falls to about 3.00 mA while the voltage across the 2.2 k rises to about 6.59 V: one fewer path, so more resistance, less current and a smaller share of the drop left for the 1 k.
How the battery and the resistors are modeled
A battery is a voltage behind a resistance.
Every resistor is solved with the rest of the circuit by nodal analysis, so a network of any shape gives the voltages and currents a bench would. The 9 V battery is a source of about 9.6 V, what a fresh alkaline one reads with nothing on it, behind 1.7 ohms of internal resistance, which is why its terminals read a little under that with a load. Set its charge to 50 percent and it reads about 7.20 V; a four-AA pack reads 6.40 V. The meter on amps has a 1 ohm shunt, small enough to change nothing here.
What it leaves out: the battery never runs down while the circuit runs (its charge is a setting, not a clock), and its resistance does not rise as it empties. Resistors have no tolerance and no temperature, so a 2.2 k is exactly 2.2 k, where a bag of real ones spreads by a few percent.
Questions
Is it free?
Yes. The circuit on this page, every part in it and the editor it opens in are on the free plan, with no card.
Do I need an account?
No. The circuit runs the moment the page does, and the editor opens without one. A free account is only for saving a project to the cloud and sharing it by link.
How do I work out resistors in parallel?
For two, multiply them and divide by their sum: 2.2 k and 4.7 k give 1.50 k. For more, add the reciprocals and take the reciprocal of the total. The answer is always less than the smallest resistor, because every branch is another path for current.
Is the current the same everywhere in a series circuit?
Yes. A series path has only one way around, so the same current goes through every part in it; here the 1 k carries the battery’s whole 3.84 mA. The voltage is what divides between the parts.
Can I simulate batteries in series and in parallel?
Yes. The battery part comes as a 9 V, two, three or four AA cells, or one or two 18650 lithium cells, and you can wire several together. Each has its own internal resistance, so a meter shows the sag under load.
More simulators
Each one opens on a circuit that is already running.
Measure a resistor network
Open the circuit, move a meter and change a resistor. Nothing to install, and no account needed.