IEC Electrical Theory and Principles 5

Question 1

The time constant (τ) of an RL circuit is defined as:

Accepted Answer

τ = L / R

Answer

The time constant of an RL circuit is τ = L/R, representing the time for current to reach approximately 63.2% of its final value.

Question 2

What is the phase angle in a circuit with R = 30 Ω and XL = 40 Ω?

Accepted Answer

53.1°

Answer

θ = arctan(XL/R) = arctan(40/30) = arctan(1.333) ≈ 53.1°.

Question 3

Reactive power in an AC circuit is measured in:

Accepted Answer

Volt-amperes reactive (VAR)

Answer

Reactive power, which represents energy stored and released by inductors and capacitors, is measured in volt-amperes reactive (VAR).

Question 4

A 240V circuit draws 20A with a power factor of 0.8. What is the true power consumed?

Accepted Answer

3840 W

Answer

True power P = V × I × PF = 240 × 20 × 0.8 = 3840 W.

Question 5

Which of the following materials is classified as a semiconductor?

Accepted Answer

Silicon

Answer

Silicon is a semiconductor, having electrical conductivity between that of conductors and insulators.

IEC - Independent Electrical Contractors Practice Test