PC Electrical Theory & Principles 4

Question 1

In an AC circuit, the opposition to current flow caused by an inductor is called:

Accepted Answer

Inductive reactance

Answer

Inductive reactance (XL = 2πfL) is the opposition an inductor presents to AC current, measured in ohms.

Question 2

Power factor in an AC circuit is defined as the ratio of:

Accepted Answer

True power to apparent power

Answer

Power factor = True Power (W) ÷ Apparent Power (VA), ranging from 0 to 1.

Question 3

A single-phase transformer has a primary winding of 480V with 400 turns and a secondary with 100 turns. What is the secondary voltage?

Accepted Answer

120V

Answer

Vs = Vp × (Ns/Np) = 480 × (100/400) = 480 × 0.25 = 120V.

Question 4

In an AC circuit containing only resistance, the voltage and current are:

Accepted Answer

In phase

Answer

Pure resistive loads cause no phase shift — voltage and current reach their peaks simultaneously.

Question 5

What happens to inductive reactance (XL) when the frequency of the applied AC voltage doubles?

Accepted Answer

It doubles

Answer

XL = 2πfL; doubling frequency doubles XL since inductance L remains constant.

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