Electrical Circuits and Network Analysis
Core concepts
Master Ohm's and Kirchhoff's laws first, then mesh and nodal analysis, superposition, Thevenin and Norton equivalents, and maximum power transfer. Be fluent with phasors, impedance, resonance, and power factor in single-phase AC, and with three-phase star/delta relations. Transients in RC and RL circuits (time constant, exponential response) and RLC damping cases are frequent. Two-port parameters and network theorems round out the syllabus.
Traps examiners set
- Sign conventions in mesh currents and node voltages; a reversed source polarity flips the answer.
- Confusing RMS with peak: power uses RMS, but instantaneous expressions use peak amplitude.
- In resonance, impedance is minimum in series but maximum in parallel circuits.
- Thevenin resistance is found with independent sources killed (voltage sources shorted, current sources opened), never with dependent sources simply removed.
- Superposition does not apply to power, only to voltages and currents.
Worked rule of thumb
For a series RLC at resonance, f0 = 1/(2pisqrt(LC)). Example: L = 10 mH, C = 1 uF gives LC = 1e-8, sqrt = 1e-4, so f0 = 1/(2pi*1e-4) is about 1592 Hz. Bandwidth equals f0/Q, and Q = (1/R)*sqrt(L/C). Check units carefully; most lost marks come from powers of ten, not from theory.
Practice strategy
Always redraw the circuit after each transformation, and verify a final answer by an independent method (for instance, nodal after mesh).