CEP Electrical Theory & Principles 4 — Questions and Answers
Question 1: A transformer has a turns ratio of 10:1 (primary to secondary). If the primary voltage is 480V, what is the secondary voltage?
- 4,800 V
- 480 V
- 48 V (Correct answer)
- 240 V
Correct answer: 48 V
Secondary voltage = Primary voltage / Turns ratio = 480 / 10 = 48V, as voltage is proportional to turns ratio.
Question 2: Skin effect in AC conductors causes current to concentrate:
- At the center of the conductor
- Uniformly throughout the conductor
- Toward the outer surface of the conductor (Correct answer)
- At the insulation interface only at high voltage
Correct answer: Toward the outer surface of the conductor
At higher AC frequencies, eddy currents force the current toward the conductor's outer surface, increasing effective resistance.
Question 3: Norton's equivalent circuit consists of:
- A voltage source in series with a resistance
- A current source in parallel with a resistance (Correct answer)
- A voltage source in parallel with a capacitor
- Two current sources in series
Correct answer: A current source in parallel with a resistance
Norton's Theorem represents any linear network as an equivalent current source (I_N) in parallel with a resistance (R_N).
Question 4: The relationship between charge (Q), capacitance (C), and voltage (V) is:
- Q = C / V
- Q = V / C
- Q = C × V (Correct answer)
- Q = C + V
Correct answer: Q = C × V
The fundamental capacitor equation Q = CV shows that stored charge is proportional to both capacitance and voltage.
Question 5: When a conductor moves through a magnetic field, an EMF is induced. This is described by:
- Coulomb's Law
- Ampere's Law
- Faraday's Law of Electromagnetic Induction (Correct answer)
- Gauss's Law
Correct answer: Faraday's Law of Electromagnetic Induction
Faraday's Law states that the induced EMF equals the rate of change of magnetic flux linkage through the conductor.
Question 6: In a delta-connected three-phase load, the relationship between line current and phase current is:
- I_line = I_phase
- I_line = I_phase × √3 (Correct answer)
- I_line = I_phase / √3
- I_line = I_phase × 2
Correct answer: I_line = I_phase × √3
In a delta connection, line current = phase current × √3, while line voltage equals phase voltage.
Question 7: The superposition theorem states that in a linear circuit with multiple sources, the total response is:
- The product of individual source responses
- Equal to the largest source response only
- The algebraic sum of responses due to each source acting alone (Correct answer)
- Dependent on the order sources are activated
Correct answer: The algebraic sum of responses due to each source acting alone
Superposition allows each independent source to be analyzed separately (others replaced by their internal impedances) and results summed.
CEP Electrical Theory & Principles 4
A transformer has a turns ratio of 10:1 (primary to secondary).
If the primary voltage is 480V, what is the secondary voltage?