CEA Electrical Theory & Fundamentals 4 — Questions and Answers
Question 1: An inductor in a DC circuit, after reaching steady state, acts as:
- An open circuit
- A short circuit (wire) (Correct answer)
- A capacitor
- A current limiter
Correct answer: A short circuit (wire)
At DC steady state, an ideal inductor has zero reactance and acts as a short circuit (low-resistance wire).
Question 2: What is the relationship between inductive reactance (XL) and frequency?
- XL decreases as frequency increases
- XL is unaffected by frequency
- XL increases as frequency increases (Correct answer)
- XL is inversely proportional to inductance
Correct answer: XL increases as frequency increases
XL = 2πfL, so inductive reactance increases proportionally with frequency.
Question 3: Three 120 V light bulbs are connected in series across 360 V. What voltage appears across each bulb?
- 360 V
- 60 V
- 120 V (Correct answer)
- 180 V
Correct answer: 120 V
In series, voltage divides equally among identical loads: 360/3 = 120 V per bulb.
Question 4: What is the term for the ratio of true power to apparent power in an AC circuit?
- Efficiency factor
- Power factor (Correct answer)
- Load factor
- Demand factor
Correct answer: Power factor
Power factor (PF) = True Power (W) / Apparent Power (VA), ranging from 0 to 1.
Question 5: Electrical energy is measured in:
- Watts
- Volt-amperes
- Kilowatt-hours (Correct answer)
- Joules per second
Correct answer: Kilowatt-hours
Kilowatt-hours (kWh) is the commercial unit of electrical energy; utility bills are measured in kWh.
Question 6: What is the primary purpose of a transformer?
- Convert AC to DC
- Change voltage and current levels (Correct answer)
- Store electrical energy
- Regulate frequency
Correct answer: Change voltage and current levels
A transformer uses electromagnetic induction to step voltage up or down while inversely changing current.
Question 7: In a series RLC circuit at resonance, what is true about the impedance?
- Impedance is at maximum
- Impedance equals only the resistance (Correct answer)
- Impedance is zero
- Impedance equals only the reactance
Correct answer: Impedance equals only the resistance
At resonance, XL = XC and they cancel, leaving total impedance equal to resistance only.
CEA Electrical Theory & Fundamentals 4
An inductor in a DC circuit, after reaching steady state, acts as: