Electrical Fundamentals
Core concepts
Start with electron theory and static electricity, then conduction in solids, liquids and gases, and the factors affecting resistance (length, area, material, temperature). Ohm's law and the power equation underpin everything. You must combine resistors in series and parallel, compute total resistance in mixed networks, and apply Kirchhoff's current and voltage laws. Capacitance, the capacitor's charge–voltage relationship, and series/parallel capacitors are examined. Magnetism, electromagnetism, induction, and inductance follow, then AC theory: rms versus peak, frequency and period, reactance, impedance, phase angle, and power factor. Transformers and three-phase supplies complete the syllabus.
Traps in questions
- Capacitors combine opposite to resistors - in parallel they add; in series they use the reciprocal rule.
- rms versus peak. Mains-type values quoted are rms: peak = rms × 1.414, average = 0.637 × peak.
- Resistance rises with temperature in metals but falls in most semiconductors and in carbon.
- Power factor means true power = V × I × cos φ, not V × I.
Worked example
A 12 V supply feeds 4 Ω in series with a parallel pair of 6 Ω and 3 Ω. Parallel pair: (6 × 3)/(6 + 3) = 18/9 = 2 Ω. Total: 4 + 2 = 6 Ω. Current: I = V/R = 12/6 = 2 A. Total power: P = V × I = 24 W. Voltage across the parallel pair is 2 A × 2 Ω = 4 V, so the 6 Ω branch carries 0.667 A and the 3 Ω branch 1.333 A - they sum to the 2 A supply current, confirming Kirchhoff.
Rule of thumb
Two resistors in parallel: R = product over sum. For identical resistors, parallel value = value ÷ number of resistors.