# Electric Circuit Simulation

> A free circuit builder for class: drag batteries, bulbs, resistors and meters onto a board, see current flow, compare series and parallel, see a short circuit.

Source: https://olyclass.com/simulations/electric-circuits/ · Updated 2026-11-01

This is a virtual circuit board for the whole class to watch on a projector, TV or interactive whiteboard. Drag batteries, bulbs, resistors, switches, ammeters, voltmeters, fuses and LEDs from the tray, join their ends, and the circuit runs at once: yellow dots travel along the wires to show the current, bulbs glow as brightly as their power says, and the meters show real readings. Join the two ends of a battery with a bare wire and you see a short circuit straight away: the wire glows red hot and the fuse melts.

## How to use it

- **Build:** drag a part from the tray on the left (along the bottom on a phone) onto the board. Parts connect where their ends meet on the same grid dot. Drag the end of a wire to the dot you want. Drag the end of a part to swing it round its other end.
- **Switch:** tap a switch to open or close it.
- **Read the numbers:** tap any part. The panel shows its own voltage U, current I, resistance R and power P. It also sets the battery's voltage (1.5 V to 12 V) and internal resistance, a resistor's value, the bulb type and the fuse rating.
- **Remove:** drag a part back into the tray, or press Remove in its panel. The bin button at the top clears the board.
- **Picture or diagram:** Picture shows the parts as they look. Diagram redraws the same circuit with standard symbols on squared paper.
- **Electrons:** switch it on to see the electrons (blue dots) move the opposite way to conventional current.
- **Ready-made circuits:** six along the bottom, from one bulb to a short circuit with a fuse.
- **Keyboard and projector:** the full screen button in the top right makes text and buttons bigger. N picks the next part, the arrow keys move it, R turns it, Space flips a switch, Delete removes it.

## Current, voltage and Ohm's law

An electric current is a flow of charged particles. In a metal wire those are electrons. By convention, current flows from the positive (+) end of the battery, round the circuit, to the negative (−) end. Electrons are negative, so they actually drift the other way. The Electrons button shows both.

Three quantities to know:

- **Current I**, in amperes (A), measured with an ammeter connected **in series**.
- **Voltage U** (often written V), in volts (V), measured with a voltmeter connected **in parallel**, across the part.
- **Resistance R**, in ohms (Ω): how much a part holds back the current.

Ohm's law: the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance: **I = U / R**. Electrical power is **P = U × I**. The more power a bulb takes, the brighter it glows, and the simulation draws each bulb's glow from exactly that power.

## Series and parallel circuits

| | Series | Parallel |
|---|---|---|
| Current | The same everywhere: I = I₁ = I₂ | The main current splits: I = I₁ + I₂ |
| Voltage | Shared: U = U₁ + U₂ | The same across each branch: U = U₁ = U₂ |
| Total resistance | R = R₁ + R₂ | 1/R = 1/R₁ + 1/R₂ |
| One bulb removed or blown | Everything goes off | The others stay on |
| Two 6 V – 6 W bulbs on 6 V | 3 V, 0.5 A, 1.5 W each: dim | 6 V, 1 A, 6 W each: full brightness; 2 A from the battery |

That is why the lights in a house are wired in parallel.

## Short circuits and fuses

A short circuit happens when the two ends of a source are joined by a path with almost no resistance. Then only the battery's small internal resistance r limits the current, so it becomes huge: I = EMF / r. Wires heat up fast, their insulation can melt, and fires start. A fuse is a thin wire in series with the circuit: when the current goes above its rating, the fuse wire melts and opens the circuit. An ammeter connected across a bulb, or straight across the battery, is a short circuit too, because it has almost no resistance: a common mistake the simulation shows safely.

Real-life safety: never try a short circuit with real batteries, sockets or car batteries. The simulation is here so students can see it without anyone getting burnt.

## Try this, with real numbers

1. Choose One bulb (6 V battery, a 6 V – 6 W bulb, so R = 6 Ω) and tap the bulb: U = 6 V, I = 1 A, P = 6 W, just as I = U / R = 6 / 6 says.
2. Choose Series vs parallel. On the left each bulb gets only 0.5 A and 1.5 W, a quarter of its rated power, so it is much dimmer. On the right each bulb takes 1 A and the battery gives 2 A.
3. Choose Ammeter and voltmeter, tap the battery and set its internal resistance r to 2 Ω. The ammeter reads I = 6 / (6 + 2) = 0.75 A. The voltmeter reads U = 6 − 0.75 × 2 = 4.5 V, which is also the voltage between the battery's terminals: less than its 6 V EMF. That is Ohm's law for the whole circuit, from upper secondary physics.
4. Choose Short circuit and fuse, tap the battery, set r = 0.5 Ω and close the switch. The current jumps to I = 6 / 0.5 = 12 A, six times the fuse's 2 A rating, and the fuse melts at once.

## Teaching ideas

The simulation fits the electricity units of middle school science and introductory physics, such as the electricity topic of GCSE Physics: circuit symbols, current and voltage, Ohm's law, series and parallel circuits, power and electrical safety. It also gives younger classes evidence for NGSS 4-PS3-2: electric currents carry energy from place to place.

1. **Warm-up (3 minutes):** open One bulb and open the switch. Ask: "Why did the bulb go out? Where does the current stop?"
2. **Measure (7 minutes):** choose Ammeter and voltmeter. Ask: "How is the ammeter connected? And the voltmeter?" Let students raise the battery from 1.5 V to 9 V and record U and I. U / I always comes out at 6 Ω. At 10.5 V the bulb burns out, well above its 6 V rating.
3. **Predict (7 minutes):** before choosing Series vs parallel, ask: "Which pair of bulbs will be brighter?" Take a vote, then press it. Tap each bulb to read U, I and P.
4. **The dangerous mistake (5 minutes):** choose Short circuit and fuse and ask: "What happens when I close the switch?" Then press Replace on the fuse and try connecting the ammeter across the bulb.
5. **Review (10 minutes):** make a review game: the whole class plays on the same screen in teams, with your phone as the remote.

## Questions teachers ask

### Are the numbers in the simulation right?

Yes, by the textbook formulas. Every time the circuit changes, the whole circuit is solved again with nodal analysis, so the numbers are right even for networks like a Wheatstone bridge. Wires, switches and ammeters are ideal, voltmeters have infinite resistance, and a bulb's resistance stays fixed, as textbooks assume. In real life a filament's resistance rises as it heats up, so real readings differ a little.

### Why are two bulbs in series dimmer?

In series the two bulbs share the battery's voltage: each 6 Ω bulb gets only 3 V, the current drops to 0.5 A, and each bulb takes 3 × 0.5 = 1.5 W, a quarter of its 6 W rating. In parallel each bulb gets the full 6 V and glows normally.

### What is a short circuit, and why is it dangerous?

A short circuit is a path between the two ends of a source with almost no resistance. The current becomes very large, the wires heat up and can start a fire. That is why home wiring always has fuses or circuit breakers that cut the power when the current is too high.

### What is the difference between conventional current and electron flow?

Conventional current is said to flow from + round the circuit to −. Electrons are negative, so they move the opposite way, from − to +. Switch on Electrons to see blue dots moving against the yellow ones.

### Do I need to install anything, and does it work on a touch board?

No installing and no sign-up: it runs in the browser and it's free. On an interactive whiteboard every finger drags its own part, so two students can build at the same time. On a phone the parts tray sits along the bottom; swipe it sideways to see them all.

[Make a review game](https://olyclass.com/create?subject=science&grade=9&topic=Electric%20circuits:%20current,%20voltage,%20resistance,%20Ohm%27s%20law,%20series%20and%20parallel%20circuits)

## Credits

Simulation and drawings made by Oly. The circuit is solved with modified nodal analysis after every change. Wires, closed switches and ammeters are ideal (zero resistance), voltmeters are ideal (infinite resistance), and a bulb's resistance stays fixed, as textbooks assume.