Electricity is invisible, which is why circuits are hard to picture at first. In this simulator you build series, parallel and series-parallel circuits with a battery, bulbs, resistors, a switch and a fuse, and you see straight away how the brightness of each bulb changes. Burn out a bulb in a series circuit and the others go off; do it in parallel and they stay on. The ammeter and the voltmeter measure current and voltage anywhere in the circuit, so you can check Ohm's law with real numbers. I also added a mode to predict what will happen before you see it, a step-by-step solver and a practice mode with instant feedback.
