Basic electrical engineering starts with electric charge, current, potential difference, energy, power and circuit laws. These quantities describe what a circuit does; components such as resistors, capacitors and inductors determine how voltage and current relate over time. The article groups below introduce each topic before moving to AC phasors and component types.
Use one symbol and SI unit for each quantity. Current is measured in amperes, potential difference in volts, resistance in ohms, capacitance in farads and inductance in henries. A component name is not the same as its property: a resistor has resistance, a capacitor has capacitance and an inductor has inductance. Phasor diagrams represent sinusoidal steady-state magnitude and phase; they do not replace time-domain analysis for every waveform.
