IEC Electrical Theory and Principles 3

Question 1

A 10 µF capacitor is connected to a 120V, 60 Hz supply. What is the capacitive reactance?

Accepted Answer

265 Ω

Answer

Xc = 1/(2πfC) = 1/(2π × 60 × 10×10⁻⁶) ≈ 265 Ω.

Question 2

What is the power factor of a purely resistive circuit?

Accepted Answer

1.0

Answer

A purely resistive circuit has voltage and current in phase, giving a power factor of 1.0 (unity).

Question 3

Kirchhoff's Current Law (KCL) states that:

Accepted Answer

The sum of currents entering a node equals the sum leaving it

Answer

KCL states that the algebraic sum of all currents at any node in a circuit equals zero (current in = current out).

Question 4

Two 100 Ω resistors are connected in parallel. What is the equivalent resistance?

Accepted Answer

50 Ω

Answer

For two equal resistors in parallel, Req = R/2 = 100/2 = 50 Ω.

Question 5

Which formula correctly expresses electrical power in terms of voltage and resistance?

Accepted Answer

P = V² / R

Answer

Substituting I = V/R into P = VI gives P = V²/R.

IEC - Independent Electrical Contractors Practice Test