Basic Electrical Fundamentals
What this domain tests
Basic Electrical Fundamentals tests voltage, current, resistance, power, Ohm’s law, and series/parallel circuits at pre-vocational level, using domestic 230 V, 50 Hz supply.
Core rules
- Voltage (V) is the potential difference in volts; current (I) is the flow in amperes; resistance (R) is opposition in ohms; power (P) is the rate of energy use in watts.
- Ohm’s law: V = I × R. Power: P = V × I = I²R = V²/R. Energy in kWh = power in kW × time in hours; one kWh is one “unit”.
- In a series circuit the current is the same through every component and the voltages add. In a parallel circuit the voltage is the same across every branch and the currents add.
- For pure resistive loads, power factor is 1. Inductive loads such as fans and motors draw a magnetising current, so P = V × I × power factor.
- A 230 V supply is nominal; measurements may be 220–240 V.
Worked example
A 60 W lamp is connected to 230 V. Current I = P ÷ V = 60 ÷ 230 = 0.26 A. Resistance R = V² ÷ P = 230² ÷ 60 = 52,900 ÷ 60 = 882 Ω. If it runs for 5 hours, energy = 0.06 kW × 5 h = 0.30 kWh, or 0.30 units.
Traps that cost marks
Mixing watts and kilowatts; using 220 V when the question states 230 V; treating a fan as a unity-power-factor load; adding resistance in parallel as if it were series; and confusing power (W) with energy (kWh).