IEC Electrical Calculations and Theory 3

Question 1

A 120V circuit has a 15Ω load. How much power does the load consume?

Accepted Answer

960W

Answer

P = V² / R = 120² / 15 = 14,400 / 15 = 960W.

Question 2

Inductive reactance (XL) increases when:

Accepted Answer

Frequency increases

Answer

XL = 2πfL, so inductive reactance is directly proportional to frequency.

Question 3

What is the apparent power (VA) of a 3-phase, 208V system drawing 25A per phase?

Accepted Answer

9,004 VA

Answer

S = √3 × V × I = 1.732 × 208 × 25 ≈ 9,004 VA.

Question 4

Two 100W, 120V incandescent lamps are connected in series across 120V. What is the total power consumed?

Accepted Answer

50W

Answer

Each lamp's resistance = 120²/100 = 144Ω; series total = 288Ω; P = 120²/288 = 50W.

Question 5

The power factor of a purely resistive circuit is:

Accepted Answer

1.0

Answer

A purely resistive circuit has no reactive power, so PF = real power / apparent power = 1.0.

IEC - Independent Electrical Contractors Practice Test