Electronic Components and Passive Networks
Electronic Components and Passive Networks tests identification, ratings, and network behaviour of resistors, capacitors, inductors, and transformers. Questions often combine colour codes, tolerances, series–parallel reduction, time constants, and AC impedance.
Core rules
- Resistor colour code: first two bands are digits, third is multiplier, fourth is tolerance; gold = ±5%, silver = ±10%.
- Capacitor codes use picofarads: 104 means 10 × 10^4 pF = 100 nF.
- Series resistance adds; parallel resistance uses reciprocal sum. Capacitors do the opposite: parallel adds, series uses reciprocal sum.
- RC charging: V(t) = Vs(1 − e^(−t/RC)); after one τ the capacitor reaches 63.2% of final value.
- Inductor current cannot change instantly; RL time constant is τ = L/R.
- Series resonance occurs at f = 1/(2π√(LC)), where XL = XC and impedance is minimum.
Worked example
A 12 V supply feeds a 10 kΩ series resistor and a 20 kΩ resistor to ground. Unloaded output across the 20 kΩ is 12 × 20/(10+20) = 8 V. Connect a 20 kΩ load across the output: the lower resistance becomes 20 kΩ || 20 kΩ = 10 kΩ. Output falls to 12 × 10/(10+10) = 6 V. The 2 V drop is the loading error.
Traps
Using the unloaded divider formula with a low-resistance load is the classic error. Reversing capacitor series/parallel rules costs marks. Ignoring capacitor voltage rating and electrolytic polarity is unsafe. In AC networks, treating reactance as constant resistance fails because XC = 1/(2πfC) and XL = 2πfL.