Basic Electronics and Electrical Fundamentals
This domain checks whether you can analyse simple DC/AC circuits, identify components, and apply network laws to telecom hardware faults. Expect numerical questions on resistors, capacitors, diodes, transistors and power.
Core rules
- Ohm's law: V = IR; power: P = VI = I²R = V²/R.
- Series resistances add; parallel conductances add: 1/R = 1/R1 + 1/R2.
- Kirchhoff's current law (node) and voltage law (loop) solve multi-branch circuits.
- Capacitive reactance Xc = 1/(2πfC); inductive reactance XL = 2πfL.
- Silicon diode drop ≈ 0.7 V, germanium ≈ 0.3 V; a Zener in reverse breakdown regulates voltage.
- BJT current gain β = Ic/Ib; the active region is used for amplification, saturation/cut-off for switching.
Worked example
A 12 V supply feeds a 470 Ω resistor in series with an LED whose forward drop is 2 V. Current I = (12 − 2)/470 = 10/470 ≈ 21.3 mA. Resistor power = I²R = (0.0213)² × 470 ≈ 0.213 W, so choose a 0.5 W resistor, not a 0.25 W part. The LED stays within a typical 20–30 mA rating.
Traps that cost marks
- Using peak voltage where RMS is required; for a sine wave Vrms = Vpeak/√2.
- Forgetting capacitor voltage rating and polarity of electrolytic capacitors.
- Confusing resistance colour-code tolerance bands (gold ±5%, silver ±10%).
- Treating a diode as ideal when the question expects the 0.7 V drop.
- Mixing units: mA with kΩ gives volts, but mA with Ω does not.
Exam approach
Draw the equivalent circuit, mark knowns, then solve. For power, calculate current first rather than guessing a formula. Check whether the component is rated for the computed power and voltage.