Basic Electrical and Electronics Engineering
This section covers Basic Electrical and Electronics Engineering: current, voltage, resistance, power, series and parallel circuits, AC and DC, transformers, semiconductors, earthing and protective devices. The exam tests simple circuit calculation and safe practice.
Core rules
- Ohm’s law: V = IR. Power: P = VI = I²R = V²/R. Energy in kWh = power in kW × time in hours.
- In series, current is common and resistances add; voltage divides. In parallel, voltage is common, current divides, and 1/Rp = 1/R1 + 1/R2.
- A fuse or MCB protects against overcurrent; it must be in the live conductor, not the neutral or earth. Earthing gives fault current a low-resistance path and operates protection.
- A transformer works on AC only and changes voltage and current, not frequency or power (apart from losses). A diode conducts one way; an LED needs a series resistor.
- Treat electricity as live until isolated, locked, tested and proven dead.
Worked example
Two resistors, 6 Ω and 3 Ω, are connected in parallel across 12 V. Rp = (6×3)/(6+3) = 2 Ω. Total current = V/Rp = 12/2 = 6 A. Branch currents are 12/6 = 2 A and 12/3 = 4 A, which sum to 6 A. Total power = VI = 72 W, or 12²/2 = 72 W.
Traps
Do not add parallel resistances directly. Do not use a fuse in the earth wire. Do not assume a transformer works on DC. Do not confuse kWh with kW: a 2 kW heater for 3 h uses 6 kWh.