Electrical and Computer Engineering
What to master
Circuit fundamentals: Ohm's law, series/parallel reduction, Kirchhoff's current and voltage laws, node and mesh analysis, superposition, Thevenin and Norton equivalents, maximum power transfer. AC: phasors, impedance of R, L and C, RMS versus peak values, real/reactive/apparent power, power factor and correction, three-phase relationships (line vs phase voltage and current, total power = sqrt(3)V_LI_L*cos theta), transformers and turns ratio, and DC/AC motor basics. Electronics: ideal op-amp rules (no input current, zero differential voltage with negative feedback), diodes, transistors as switches. Digital: number systems and binary/hex conversion, two's complement, Boolean algebra and simplification, combinational logic, flip-flops, counters, and basic computer architecture concepts.
Traps
- Quoting RMS where the problem specifies peak (V_rms = V_peak/sqrt(2) for sinusoids).
- Mixing real power (W), reactive power (var) and apparent power (VA); only real power does work.
- Assuming an ideal op-amp without negative feedback -- the virtual-short rule fails.
- Sign errors in two's complement and in KVL loop directions.
Worked example
A single-phase load draws 10 A RMS at 240 V RMS with a power factor of 0.8 lagging. Real power P = VIcos theta = 240100.8 = 1920 W; apparent power is 2400 VA and reactive power is 1440 var.
Rule of thumb: convert everything to RMS and phasor form before combining impedances; then the real power is the real part of S = VI, and losses follow from I^2*R only.