Electrical Fundamentals — Construction Electrician (309A) Practice Questions

Free Electrical Fundamentals practice questions

1. 1.What is Ohm's Law?

   • A.P = I × E
   • B.E = I × R✓
   • C.I = E × R
   • D.R = I × E

   Why: Ohm's Law: E = I × R (Voltage = Current × Resistance). Also expressed as I = E/R and R = E/I. Fundamental to all electrical calculations.

2. 2.What is the power factor of a purely resistive load?

   • A.0
   • B.0.5
   • C.0.8
   • D.1.0 (unity)✓

   Why: Pure resistance: voltage and current are in phase = power factor of 1.0 (unity). Inductive loads (motors) have lagging PF; capacitive loads have leading PF.

3. 3.The unit of measurement for capacitance is:

   • A.Henry
   • B.Ohm
   • C.Farad✓
   • D.Watt

   Why: Capacitance is measured in Farads (F). Practical units are microfarads (µF) and picofarads (pF). Henry = inductance. Ohm = resistance.

4. 4.What happens to current flow when resistance increases in a DC circuit (voltage constant)?

   • A.Current increases
   • B.Current decreases✓
   • C.Current stays the same
   • D.Current reverses

   Why: Ohm's Law: I = E/R. If R increases and E is constant, current decreases. They are inversely proportional.

5. 5.What is the reactance of a 50µF capacitor at 60Hz?

   • A.53.1Ω✓
   • B.5.3Ω
   • C.530Ω
   • D.0.053Ω

   Why: XC = 1 ÷ (2π × f × C) = 1 ÷ (6.2832 × 60 × 0.00005) = 1 ÷ 0.01885 = 53.1Ω

6. 6.What is the impedance of a circuit with R=30Ω and XL=40Ω?

   • A.70Ω
   • B.10Ω
   • C.50Ω✓
   • D.35Ω

   Why: Z = √(R² + XL²) = √(900 + 1600) = √2500 = 50Ω. Impedance is the vector sum of resistance and reactance.

7. 7.Frequency of the Canadian power grid is:

   • A.50 Hz
   • B.60 Hz✓
   • C.120 Hz
   • D.240 Hz

   Why: North America uses 60 Hz. Europe and most of Asia use 50 Hz. The frequency determines motor speed and transformer design.

8. 8.What type of meter measures resistance?

   • A.Voltmeter
   • B.Ammeter
   • C.Ohmmeter (or multimeter in Ω mode)✓
   • D.Wattmeter

   Why: An ohmmeter sends a small test current through the circuit and measures the resistance. Always de-energize the circuit before measuring resistance.

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