Electrical Theory and Circuit Fundamentals
Core concepts
Candidates must be fluent with Ohm's law (V = IR), power relationships (P = VI = I²R = V²/R), and the behaviour of series and parallel networks. Know that in a series circuit current is common and voltages sum, while in parallel the voltage is common and branch currents sum. Understand resistance in conductors (R = ρL/A) and how length, cross-sectional area and temperature affect it. Appreciate AC fundamentals: RMS versus peak values, frequency, phase, and the difference between resistive, inductive and capacitive loads, including power factor and the relationship between true, reactive and apparent power.
Traps in questions
Common distractors include confusing RMS with peak (V_rms = V_peak/√2), mixing up series and parallel rules, and forgetting that power factor affects current for a given kW load. Watch for questions that assume unity power factor without stating it, and for unit slips (mA versus A, kΩ versus Ω). Another trap is treating conductor resistance as negligible when the question supplies resistivity and dimensions.
Worked example / rule of thumb
A 2 kW resistive heater on 230 V draws I = P/V = 2000/230 ≈ 8.7 A. If the same 2 kW load had a power factor of 0.8, apparent power S = P/pf = 2.5 kVA and current I = S/V ≈ 10.9 A. Rule of thumb: always convert kW to VA using power factor before calculating current on AC loads. For quick checks, remember 1 kW at 230 V unity pf is about 4.35 A.