Electrical FE Exam: Common Mistakes

Resistors in series add directly (R_total = R1 + R2 + ...). Resistors in parallel combine as reciprocals (1/R_total = 1/R1 + 1/R2 + ...). For capacitors, the rules reverse: capacitors in parallel add directly, and capacitors in series combine as reciprocals. Double-check which configuration the circuit shows.

In AC analysis, every voltage and current has both magnitude and phase. When adding voltages or currents, you must use phasor addition (complex number addition), not scalar addition. Simply adding magnitudes ignores phase differences and gives incorrect results for most AC circuits.

Choose the node connected to the most branches as your reference (ground) node. A poor reference node choice leads to more complex equations and increases the chance of algebraic errors. Also ensure you write KCL equations for every non-reference node to get a solvable system.

When using superposition, you can only turn off independent sources (voltage sources become short circuits, current sources become open circuits). Dependent sources must remain active in every superposition step. Turning off a dependent source is a fundamental error that invalidates the analysis.

Power calculations use RMS values, while oscilloscope readings often show peak values. For sinusoidal signals, V_rms = V_peak / sqrt(2). Many exam problems mix peak and RMS values in the same problem to test whether you convert correctly before calculating power or other quantities.