Basic Electricity and Electronics for Telecom
Basic Electricity and Electronics for Telecom
This domain tests whether you can apply electrical laws to telecom circuits and recognise common electronic components. Expect numerical questions on Ohm's law, series and parallel networks, power, AC amplitude, and simple diode or transistor circuits.
Core rules
- Ohm's law: V = IR; power: P = VI = I²R = V²/R.
- Series: same current, resistances add, voltages divide in proportion to resistance.
- Parallel: same voltage, reciprocal resistance adds; two resistors give R = R1R2/(R1+R2).
- For AC, RMS values are used for power; peak = RMS × √2 for a sine wave.
- A diode conducts when forward biased above its knee voltage; an LED needs a series resistor to limit current.
Worked example
A 12 V supply feeds 220 Ω and 330 Ω in series. Total R = 550 Ω, so I = 12/550 = 0.0218 A = 21.8 mA. Voltage across 220 Ω = 0.0218 × 220 = 4.8 V; across 330 Ω = 7.2 V. Total power = 12 × 0.0218 = 0.262 W. If the 220 Ω resistor is replaced by a parallel pair of 440 Ω, the branch is 220 Ω, so current rises and the voltage division changes; always recalculate the equivalent resistance first.
Traps that cost marks
Mixing mA and A; adding parallel resistances directly; using peak voltage where RMS is required; forgetting diode polarity; and ignoring resistor power rating. In telecom PCBs, a correct value with the wrong power rating can still fail.