Electrical Fundamentals: Circuits, Magnetism, AC/DC and Measurement
Candidates must be fluent with Ohm's law (V = IR), power (P = VI = I²R = V²/R), and series and parallel circuit behaviour. In series, current is common and voltages add; in parallel, voltage is common and currents add. Kirchhoff's voltage and current laws formalise this. Resistance of a conductor rises with length and resistivity and falls with cross-sectional area: R = ρL/A.
Magnetism underpins machines and transformers: current creates a magnetic field, a changing field induces an EMF (Faraday), and Lenz's law gives the direction opposing change. Understand flux, flux density, reluctance and the right-hand grip rule.
AC theory requires peak, RMS and average values, frequency, period, phase, and the relationships in resistive, inductive and capacitive circuits. Know that inductive reactance rises with frequency and capacitive reactance falls, that current lags voltage in an inductor and leads in a capacitor, and that power factor is the cosine of the phase angle. Real power is watts, reactive power is VAR, apparent power is VA.
Measurement traps: a voltmeter goes in parallel and an ammeter in series (an ammeter in parallel can blow its fuse or short the circuit); a clamp meter measures current without breaking the circuit; a multimeter's CAT rating must suit the installation; true RMS matters for distorted waveforms. Insulation resistance uses a high-voltage DC tester, not a standard multimeter.
Worked example: a 2.4 kW resistive load on 240 V draws I = P/V = 10 A, and R = V/I = 24 Ω. A 10 A load on a 230 V circuit with 0.5 Ω total conductor resistance drops 5 V, about 2.2 percent.