CEA Electrical Theory & Fundamentals 3 — Questions and Answers
Question 1: What is the frequency of standard AC power in the United States?
- 50 Hz
- 60 Hz (Correct answer)
- 25 Hz
- 400 Hz
Correct answer: 60 Hz
The US power grid operates at 60 Hz, meaning AC current completes 60 cycles per second.
Question 2: Two resistors of 10 Ω and 15 Ω are connected in series across 50 V. What is the voltage across the 10 Ω resistor?
- 20 V (Correct answer)
- 30 V
- 25 V
- 15 V
Correct answer: 20 V
Total R = 25 Ω, I = 50/25 = 2 A, V10 = 2 × 10 = 20 V.
Question 3: The opposition to current flow offered by a capacitor is called:
- Resistance
- Inductance
- Capacitive reactance (Correct answer)
- Impedance
Correct answer: Capacitive reactance
Capacitive reactance (Xc) is the opposition capacitors present to AC current, measured in ohms.
Question 4: If a circuit draws 15 A at 240 V, what is the power consumption in kilowatts?
- 3.6 kW (Correct answer)
- 2.4 kW
- 1.6 kW
- 4.8 kW
Correct answer: 3.6 kW
P = V × I = 240 × 15 = 3,600 W = 3.6 kW.
Question 5: Which law states that the induced EMF in a conductor is proportional to the rate of change of magnetic flux?
- Ampere's Law
- Coulomb's Law
- Faraday's Law (Correct answer)
- Lenz's Law
Correct answer: Faraday's Law
Faraday's Law states EMF = -dΦ/dt, meaning induced voltage equals the rate of change of magnetic flux.
Question 6: What is the peak voltage of a 120 V RMS AC supply?
- 120 V
- 169.7 V (Correct answer)
- 84.8 V
- 240 V
Correct answer: 169.7 V
Peak voltage = RMS × √2 = 120 × 1.414 ≈ 169.7 V.
Question 7: What does a higher AWG number indicate about a wire?
- Larger diameter and higher current capacity
- Smaller diameter and lower current capacity (Correct answer)
- Higher voltage rating
- Greater insulation thickness
Correct answer: Smaller diameter and lower current capacity
In the American Wire Gauge system, higher numbers indicate thinner wire with lower current-carrying capacity.
CEA Electrical Theory & Fundamentals 3
What is the frequency of standard AC power in the United States?