Basic Electrical Concepts and Fundamentals
Basic Electrical Concepts and Fundamentals is the foundation domain: the exam checks whether you can apply Ohm's law, power and energy relationships, series-parallel reduction, AC RMS values and power factor to vocational installation problems.
Core rules
- Ohm's law: V = IR; for a conductor R = ρL/A, so resistance rises with length and falls with area.
- Power: P = VI = I²R = V²/R for DC and resistive AC; single-phase AC uses P = VI cos φ, three-phase P = √3 V_L I_L cos φ.
- Energy in kWh = kW × hours; tariff is charged per kWh (unit).
- Series: same current, voltages add, R_total = R1 + R2. Parallel: same voltage, currents add, 1/R_total = 1/R1 + 1/R2.
- For sine AC, V_rms = V_peak/√2 and form factor = 1.11.
Worked example
A 2 kW, 230 V geyser runs for 1.5 h. Current I = 2000/230 = 8.70 A. Element resistance R = V²/P = 230²/2000 = 26.45 Ω. Energy = 2 kW × 1.5 h = 3 kWh. At ₹7.50 per unit, cost = 3 × 7.50 = ₹22.50. If a 2 kW three-phase motor at pf 0.85 were supplied at 415 V, line current would be 2000/(√3 × 415 × 0.85) = 3.27 A, showing why three-phase currents are smaller.
Traps
Do not write kW when the answer is kWh; do not use peak voltage in power formulae; do not ignore power factor for motors; and in voltage-drop or resistance sums, use the total conductor length, not one-way length.