Electric circuits

How it works

Current flows only through a closed circuit. A resistor follows Ohm’s law: current is proportional to voltage and inversely proportional to resistance. In a series circuit the same current flows through every component and the voltage is shared; in a parallel circuit each branch has the same voltage and the currents add up. An ammeter is connected in series, a voltmeter in parallel. A capacitor charges through a resistor gradually, at a rate set by the time constant τ = R·C.

U = R·Iseries: R = R₁ + R₂parallel: 1/R = 1/R₁ + 1/R₂τ = R·C

Try it yourself

1. In “Lamp and switch”, change “Filament resistance” from 30 to 60 Ω. Predict the ammeter reading first: the current halves, from about 0.2 A to 0.1 A.
2. Compare “Series circuit” and “Parallel circuit” with the same parts (12 V, 100 Ω and 200 Ω). In series 40 mA flows; in parallel the source supplies 180 mA.
3. In “LED and series resistor”, reduce the resistor from 220 Ω to 100 Ω. The LED current rises from about 13 mA to 29 mA and the simulation warns about overload above 20 mA.
4. In “Charging a capacitor” (1 kΩ, 1,000 µF, so τ = 1 s), select the capacitor and read from the voltage graph that it reaches about 63 % of the supply voltage after 1 s.

Model limitations

This is a teaching model with ideal components: sources have 0.1 Ω internal resistance, wires 0.01 Ω, LEDs and diodes use a simplified threshold model and the lamp has a constant resistance. AC circuits with inductors and capacitors use a second-order method with fine sub-steps. It is not a design tool for real devices; keep mains-voltage experiments virtual.

Related experiments

• RLC circuits
• Logic circuits
• Atoms and chemical bonds