AC circuit construction kit – build RLC circuits

What it shows

A virtual circuit construction kit for the topic of alternating current: students drag components from the toolbox onto the board and join free wire ends into any circuit they like — series, parallel, several sources — instead of just looking at a printed diagram. The circuit is solved in real time by nodal analysis, so every arrangement gives correct readings.

How to use

The Intro screen has an AC source with adjustable amplitude and frequency, batteries, resistors, light bulbs and switches: electrons move back and forth, reversing with the source, and bulbs flicker with the instantaneous power. A voltmeter, an ammeter and two time graphs have probes that can be dragged anywhere in the circuit. The Lab screen adds capacitors, inductors, fuses, internal resistance, wire resistance and a stopwatch: place both graphs on the same capacitor to see i lead u by 90°, or on an inductor to see i lag; use a battery and a switch to time a capacitor charging to 63 % (τ = RC). When a component is selected, the readout puts the simulated values next to the phasor solution: impedance Z = √(R² + (Z_L − Z_C)²), amplitude I₀ = U₀/Z and the phase difference. For example, in the series R–L–C preset (R = 10 Ω, L = 5 H, C = 0.05 F, U₀ = 10 V) the resonant frequency is f₀ = 1/(2π√(LC)) ≈ 0.32 Hz, where the peak current reaches 1 A and is in phase with the voltage; at 0.5 Hz the amplitude drops to about 0.73 A and i lags by about 43°.

Parameters you can change

• Screen Intro, Lab
• Starting circuit (circuits with a capacitor/inductor open the Lab screen) Empty board, AC source + bulb, Series R–C (AC), Series R–L (AC), Series R–L–C (resonance), Charging: battery + switch + R + C, Inductor: battery + switch + bulb + L
• AC source voltage amplitude U₀ 0–120 V
• AC source frequency 0.1–2 Hz
• Battery voltage 0–120 V
• Resistance R 0–120 Ω
• Capacitance C 0.01–0.2 F
• Inductance L 0.1–10 H
• Wire resistivity (Lab) 0–1 Ω/m
• Show current as Electrons, Conventional current
• Component symbol style Lifelike, Schematic
• Show component labels
• Show component values
• Show voltmeter
• Show ammeter
• Show voltage–time graph
• Show current–time graph
• Show stopwatch (Lab)

Questions to explore

1. Why does a bulb connected to a low-frequency AC source flicker twice in every cycle?
2. With both graphs on the same capacitor, does the peak of i come before or after the peak of u? What about an inductor?
3. In a series circuit, do the voltage amplitudes across R, L and C add up to the amplitude of the source voltage? Why?