CEP Electrical Theory & Principles 3 — Questions and Answers
Question 1: Which of the following best describes impedance in an AC circuit?
- The DC resistance only
- The opposition to current flow from resistance alone
- The total opposition to AC current flow combining resistance and reactance (Correct answer)
- The ratio of voltage to reactive power
Correct answer: The total opposition to AC current flow combining resistance and reactance
Impedance (Z) is the complex combination of resistance (R) and reactance (X), expressed in ohms: Z = √(R² + X²).
Question 2: In a three-phase balanced system, the phase voltage is related to the line voltage by:
- V_line = V_phase × √3 (Correct answer)
- V_line = V_phase / √3
- V_line = V_phase × 2
- V_line = V_phase / 2
Correct answer: V_line = V_phase × √3
In a balanced three-phase wye (star) system, the line voltage equals the phase voltage multiplied by √3 (≈1.732).
Question 3: The energy stored in a capacitor is expressed as:
- E = LI²
- E = ½CV² (Correct answer)
- E = CV
- E = ½LI
Correct answer: E = ½CV²
The energy stored in a capacitor is E = ½CV², where C is capacitance in farads and V is voltage in volts.
Question 4: What happens to the total capacitance when capacitors are connected in series?
- Total capacitance increases
- Total capacitance equals the largest capacitor
- Total capacitance decreases below the smallest value (Correct answer)
- Total capacitance remains unchanged
Correct answer: Total capacitance decreases below the smallest value
Series capacitors follow the reciprocal rule (1/CT = 1/C1 + 1/C2 + ...), resulting in a total less than the smallest capacitor.
Question 5: In an AC circuit, resonance occurs when:
- Resistance equals reactance
- Inductive reactance equals capacitive reactance (Correct answer)
- Voltage and current are 180° out of phase
- Power factor equals zero
Correct answer: Inductive reactance equals capacitive reactance
Resonance occurs when XL = XC, causing them to cancel, leaving only resistance to limit current, and power factor reaches unity.
Question 6: The unit of magnetic flux density is the:
- Weber (Wb)
- Tesla (T) (Correct answer)
- Henry (H)
- Farad (F)
Correct answer: Tesla (T)
Magnetic flux density (B) is measured in Tesla (T), where 1 T = 1 Wb/m², representing flux per unit area.
Question 7: Which theorem allows a complex linear circuit to be replaced by a single voltage source and series resistance?
- Norton's Theorem
- Superposition Theorem
- Thevenin's Theorem (Correct answer)
- Maximum Power Transfer Theorem
Correct answer: Thevenin's Theorem
Thevenin's Theorem simplifies any linear network to an equivalent voltage source (V_th) in series with a resistance (R_th).
CEP Electrical Theory & Principles 3
Which of the following best describes impedance in an AC circuit?