Electrical and Electronic Fundamentals
This domain checks that you can analyse a circuit rather than memorise a formula sheet: Ohm's law, series and parallel networks, power, Kirchhoff's laws, AC quantities, and the behaviour of the diode and transistor as a switch.
Rules that carry most marks
- V = IR; P = VI = I²R = V²/R.
- Series: R total = sum of resistances, current common, voltage divides.
- Parallel: 1/R total = sum of reciprocals; two resistors give R = R₁R₂/(R₁+R₂); voltage common, current divides.
- Kirchhoff: current into a node = current out; the sum of voltages around a loop = 0.
- AC: RMS = peak/√2; f = 1/T; X_L = 2πfL; X_C = 1/(2πfC).
- Silicon diode drops about 0.7 V when forward biased and blocks in reverse; a transistor used as a switch is driven into saturation or cut-off.
Worked example. A 12 V supply feeds 6 Ω and 3 Ω in parallel. R = (6 × 3)/(6 + 3) = 2 Ω, so total current I = 12/2 = 6 A. Branch currents: 12/6 = 2 A and 12/3 = 4 A, which sum to 6 A. Branch power: 24 W and 48 W, total 72 W, matching P = VI = 12 × 6 = 72 W.
Traps. Adding parallel resistances as if in series; treating the peak value as RMS (a 325 V peak is 230 V RMS); forgetting to convert mA to A before calculating; assuming an ideal voltmeter has low resistance - it must be high, while an ammeter must be low.