Electrical Fundamentals
What the module tests
Electrical fundamentals covers electron theory, static electricity, DC circuits, capacitance, magnetism, inductance, AC theory, resistors, transformers and filters. The exam expects confident use of Ohm's law, series and parallel networks, power, reactance and transformer ratios.
Core rules
- Ohm's law: V = IR. Power: P = VI = I²R = V²/R.
- Series resistances add; parallel resistances add as reciprocals.
- Capacitive reactance XC = 1/(2πfC); inductive reactance XL = 2πfL.
- In a transformer, Vp/Vs = Np/Ns; power is approximately constant, so current transforms inversely.
- RMS values are the effective values; peak = RMS × 1.414 for a sine wave.
- Current in a capacitor leads voltage by 90°; current in an inductor lags voltage by 90°.
Worked example
A 115 V RMS, 400 Hz supply is connected across a 10 µF capacitor. Find the reactance and current. XC = 1/(2π × 400 × 10 × 10⁻⁶) = 1/(0.02513) = 39.8 Ω. I = V/XC = 115/39.8 = 2.89 A. Because the load is purely capacitive, the current leads the voltage by 90°, but the magnitude is 2.89 A.
Traps
Forgetting to convert microfarads to farads; adding capacitors in parallel the resistor way (they add directly, like resistors in series); mixing RMS and peak; ignoring phase angle when adding AC voltages; assuming a transformer is loss-free when the question asks for efficiency.
Exam approach
List the known values with prefixes converted, select the formula, and check whether the question asks for magnitude, phase or both. For series AC circuits, add voltages vectorially, not arithmetically.