Electrical Fundamentals
Electrical Fundamentals
This domain tests the basic quantities and laws that every solar PV electrical task depends on: charge, current, voltage, resistance, power, energy, and series/parallel networks. Expect numerical questions using Ohm's law and Kirchhoff's laws.
Core rules
- Current is the rate of charge flow, I = Q/t, measured in amperes.
- Ohm's law: V = IR; power: P = VI = I²R = V²/R.
- Energy in kWh = power in kW × time in hours. 1 kWh = 3.6 MJ.
- Series: same current, voltages add, R_total = R1 + R2 + ...
- Parallel: same voltage, currents add, 1/R_total = 1/R1 + 1/R2 + ...
- Kirchhoff: current law at a node, voltage law around a loop.
Worked example
A 12 V battery supplies two resistors in series, 4 Ω and 6 Ω. R_total = 10 Ω; I = 12/10 = 1.2 A. Voltage across 4 Ω = 1.2 × 4 = 4.8 V; across 6 Ω = 7.2 V; sum = 12 V. Total power = 12 × 1.2 = 14.4 W, or 1.2² × 10 = 14.4 W. The 4 Ω resistor dissipates 5.76 W and the 6 Ω resistor 8.64 W.
Traps that cost marks
Using V²/R with the wrong voltage; mixing mA and A; adding parallel resistances directly; placing an ammeter in parallel or a voltmeter in series; forgetting that the largest resistor in series drops the largest voltage.