Electrical and electronic fundamentals
Electrical and electronic fundamentals is the toolbox domain: the exam checks whether you can handle units, apply Ohm's law and power formulas to DC and AC circuits, and recognise how real components behave. Questions are usually short calculations or component-identification items, so precision with prefixes and signs matters more than long theory.
Units and basic quantities
Use SI units and power-of-ten prefixes: 1 kΩ = 10³ Ω, 1 mA = 10⁻³ A, 1 pF = 10⁻¹² F. Current is charge per second (I = Q/t); 1 A = 1 C/s. Voltage is energy per charge, and resistance relates voltage to current. A common exam error is mixing milliamps with amps before calculating.
Ohm's law and power
For a resistor: V = IR, I = V/R, R = V/I. Power: P = VI = I²R = V²/R. In series, resistances add and current is common; in parallel, conductances add, and for two resistors R = R1R2/(R1+R2). Capacitors block DC and pass AC; inductors pass DC and oppose changing current. Reactance is XC = 1/(2πfC) and XL = 2πfL; at resonance XL = XC.
Worked example
A 12 V DC supply feeds a 3 Ω resistor. I = V/R = 12/3 = 4 A. P = VI = 12 × 4 = 48 W, or I²R = 16 × 3 = 48 W. If the same resistor is replaced by two 6 Ω resistors in parallel, the equivalent is 3 Ω, so current and power stay the same. If they are in series, R = 12 Ω, I = 1 A, P = 12 W. Show the equivalent-resistance step before using Ohm's law.
Traps that cost marks
- Using peak voltage where RMS is required: for a sine wave, Vrms = Vpeak/√2, and power uses RMS.
- Forgetting that I²R squares the current when converting mA to A.
- Treating a capacitor as an open circuit at every frequency; its reactance falls as frequency rises.
- Adding parallel resistors by simple addition.
- Ignoring component tolerance and power rating: a 0.25 W resistor cannot safely dissipate 1 W.