Electrical and Electronics Engineering Fundamentals
What you must command
DC circuits (Ohm's law, series/parallel, Kirchhoff's laws, Thevenin and Norton), AC fundamentals (RMS, phasors, impedance, power factor, three-phase), transformers and induction motors, and basic electronics (diodes, rectifiers, transistors, operational amplifiers, logic gates).
Traps that appear in questions
- RMS vs. peak: for a sine wave, RMS = peak/√2; average = 2×peak/π.
- Power factor: real power = VI cos φ; apparent power = VI; reactive power = VI sin φ. A low power factor means high current for the same real power.
- Three-phase: line voltage = √3 × phase voltage in star; line current = √3 × phase current in delta.
- Transformer EMF equation: E = 4.44 f N Φ_max.
- Diode drop: a silicon diode drops about 0.7 V when conducting - do not ignore it in rectifier questions.
- Op-amp ideal assumptions: infinite input impedance, zero output impedance, virtual short between inputs under negative feedback.
Worked rule of thumb
For a single-phase load of 2 kW at 230 V with power factor 0.8: I = P/(V cos φ) = 2000/(230 × 0.8) ≈ 10.9 A. Apparent power = 2000/0.8 = 2500 VA. If the power factor were corrected to unity, the current would fall to about 8.7 A - the reason utilities penalise low power factor.
For a three-phase star-connected load with phase voltage 230 V, line voltage = √3 × 230 ≈ 398 V, commonly quoted as 400 V.