NETA AC/DC Theory and Circuits 4 — Questions and Answers
Question 1: In a series RLC circuit at resonance, which statement is true?
- Impedance is at its maximum value
- Capacitive and inductive reactances are equal and cancel (Correct answer)
- Current is at its minimum value
- Power factor equals zero
Correct answer: Capacitive and inductive reactances are equal and cancel
At resonance, XL equals XC, so they cancel and the circuit impedance equals only the resistance R.
Question 2: What is the time constant (τ) for a series RC circuit with R = 10 kΩ and C = 50 µF?
- 0.5 seconds (Correct answer)
- 5 seconds
- 50 milliseconds
- 500 milliseconds
Correct answer: 0.5 seconds
τ = RC = 10,000 Ω × 50×10⁻⁶ F = 0.5 seconds.
Question 3: A transformer has 500 primary turns and 100 secondary turns. If the primary voltage is 480 V, what is the secondary voltage?
- 2,400 V
- 96 V (Correct answer)
- 480 V
- 240 V
Correct answer: 96 V
Vs = Vp × (Ns/Np) = 480 × (100/500) = 96 V.
Question 4: In a purely capacitive AC circuit, the current leads the voltage by:
- 0°
- 45°
- 90° (Correct answer)
- 180°
Correct answer: 90°
In a purely capacitive circuit, current leads voltage by exactly 90° (π/2 radians).
Question 5: Which type of circuit connection results in the same voltage across each element but different currents?
- Series circuit
- Parallel circuit (Correct answer)
- Series-parallel circuit
- Delta-connected circuit
Correct answer: Parallel circuit
In a parallel circuit, all branches share the same voltage while current divides among the branches.
Question 6: The quality factor (Q) of an inductor is defined as the ratio of:
- Inductive reactance to resistance (Correct answer)
- Resistance to inductive reactance
- Capacitive reactance to inductive reactance
- Impedance to resistance
Correct answer: Inductive reactance to resistance
Q = XL / R, representing how efficiently an inductor stores energy relative to its losses.
Question 7: When measuring DC voltage with a digital multimeter across a 24 V battery showing 22.8 V, what does this most likely indicate?
- The meter is faulty
- The battery is fully charged
- The battery is partially discharged (Correct answer)
- The meter leads are reversed
Correct answer: The battery is partially discharged
A reading of 22.8 V on a nominal 24 V battery indicates the battery is partially discharged but not critically low.
NETA AC/DC Theory and Circuits 4
In a series RLC circuit at resonance, which statement is true?