IEC Electrical Theory and Principles 2

Question 1

What is the phase relationship between voltage and current in a purely inductive circuit?

Accepted Answer

Current lags voltage by 90°

Answer

In a purely inductive circuit, current lags voltage by 90° because the inductor opposes changes in current.

Question 2

A transformer has 500 turns on the primary and 100 turns on the secondary. If the primary voltage is 240V, what is the secondary voltage?

Accepted Answer

48V

Answer

Using the turns ratio formula: Vs = Vp × (Ns/Np) = 240 × (100/500) = 48V.

Question 3

Which of the following best describes impedance in an AC circuit?

Accepted Answer

The total opposition to AC current flow including resistance and reactance

Answer

Impedance (Z) is the total opposition to AC current and is the vector sum of resistance and reactance.

Question 4

What happens to capacitive reactance as frequency increases?

Accepted Answer

It decreases

Answer

Capacitive reactance (Xc = 1/2πfC) is inversely proportional to frequency, so it decreases as frequency increases.

Question 5

In a series RLC circuit at resonance, which statement is true?

Accepted Answer

Inductive and capacitive reactances are equal and cancel

Answer

At resonance, XL = XC, they cancel each other, and the circuit impedance equals only the resistance.

IEC - Independent Electrical Contractors Practice Test