Electrical and Electronic Technology
What this domain tests
Electrical and Electronic Technology tests DC and AC circuit analysis, machine and transformer principles, basic electronics, and safe wiring practice. Expect calculations, not just descriptions.
Core rules
- Ohm's law V = IR; power P = VI = I²R = V²/R. Series resistances add; parallel conductances add, so 1/R_T = 1/R_1 + 1/R_2.
- Kirchhoff: currents at a node sum to zero; voltages around a loop sum to zero.
- AC: V_rms = V_peak/√2; reactance X_L = 2πfL and X_C = 1/(2πfC); impedance Z = √(R² + (X_L − X_C)²); power factor = cos φ, and real power P = VI cos φ.
- Transformers: V_s/V_p = N_s/N_p; power is approximately conserved, so a step-up in voltage steps down current.
- Electronics: a silicon diode drops about 0.7 V when forward biased; a transistor needs correct bias; logic gates implement Boolean functions; an op-amp with negative feedback follows its input conditions.
- Protection: fuses and MCBs protect cables, RCDs protect people from earth leakage, and earthing gives fault current a low-resistance path.
Worked example
A 6 Ω and a 3 Ω resistor are connected in parallel across 12 V. Equivalent resistance: 1/R_T = 1/6 + 1/3 = 1/2, so R_T = 2 Ω. Total current = 12/2 = 6 A. Branch currents: 12/6 = 2 A and 12/3 = 4 A, which sum to 6 A. Total power = 12 × 6 = 72 W, or 2²×6 + 4²×3 = 24 + 48 = 72 W.
Traps
Adding parallel resistors directly; using peak voltage where RMS is required; omitting power factor in AC power; ignoring the diode drop; assuming a fuse protects against electric shock; reversing transformer current and voltage ratios.