Electrical Theory and Fundamentals
What you must understand
Candidates should be fluent in Ohm's law (E = I × R), the power relationships (P = E × I, P = I²R, P = E²/R), and the difference between series and parallel circuits. Know that series circuits share current and divide voltage, while parallel circuits share voltage and divide current. Understand AC fundamentals: RMS versus peak values (RMS = peak ÷ √2), frequency, impedance, reactance, and power factor. Single-phase versus three-phase relationships matter too: in a balanced three-phase system, total power is √3 × E × I × PF, and line current relates to phase current by √3 in a wye connection.
Traps in questions
Watch for unit mix-ups (milliamps, kilowatts, kilovolt-amperes) and for questions that give you peak voltage but ask for a heating or power result, which requires RMS. Resistance questions often hide a temperature coefficient or expect you to recognize that resistance of a conductor increases with length and decreases with cross-sectional area. Power-factor questions frequently want you to distinguish true power (watts) from apparent power (volt-amperes).
Rule of thumb and worked example
For a purely resistive single-phase load, watts equal volt-amperes, so you can shortcut. Example: a 240-volt, 30-ohm resistive heater draws I = E ÷ R = 240 ÷ 30 = 8 amperes, and P = E × I = 240 × 8 = 1,920 watts. If the same circuit were inductive with a 0.8 power factor, true power would be 1,920 × 0.8 = 1,536 watts while apparent power stays 1,920 VA. Always check whether the question asks for watts or volt-amperes before choosing an answer.