Learn how electricity actually works
Nine modules: fundamentals, Ohm's Law, wiring, color codes, then capacitors, inductors, and transistors — each with a live lab — plus a practice quiz.
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Voltage & Current
Electricity is the flow of charge. Two measurements describe that flow at any point.
Voltage (V) is electrical pressure — the energy per unit charge available to push electrons through a circuit. Measured in volts.
Current (I) is how much charge flows past a point per second. Measured in amperes (amps). In metal wires, electrons drift from negative toward positive, but circuit diagrams still use conventional current: positive to negative.
Voltage
Potential difference between two points. A 9 V battery holds about 9 joules of energy per coulomb of charge.
- AA cell ≈ 1.5 V
- USB power ≈ 5 V
- Car battery ≈ 12 V
Current
Rate of charge flow. LEDs often need only a few milliamps (mA). A phone charger may supply 1–3 A.
- LED ≈ 5–20 mA
- Phone charge ≈ 1–3 A
- 1 A = 1000 mA
Closed loop required
Charge needs a complete path from one battery terminal back to the other.
- Open switch = open circuit = no current.
- Short circuit (almost zero resistance across the source) draws huge current — dangerous and can destroy the supply.
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