EETC Circuit Theory 2 — Questions and Answers
Question 1: In a series RLC circuit at resonance, what is the relationship between inductive reactance (XL) and capacitive reactance (XC)?
- XL > XC
- XL < XC
- XL = XC (Correct answer)
- XL = 2XC
Correct answer: XL = XC
At resonance in a series RLC circuit, XL equals XC, causing them to cancel out and leaving only the resistance.
Question 2: A capacitor of 100 µF is connected to a 120V, 60Hz AC source. What is its capacitive reactance?
- 26.5 Ω (Correct answer)
- 53.1 Ω
- 13.3 Ω
- 106.1 Ω
Correct answer: 26.5 Ω
XC = 1/(2πfC) = 1/(2π × 60 × 0.0001) ≈ 26.5 Ω.
Question 3: Which theorem states that any two-terminal linear network can be replaced by a single voltage source in series with an impedance?
- Norton's Theorem
- Superposition Theorem
- Thevenin's Theorem (Correct answer)
- Maximum Power Transfer Theorem
Correct answer: Thevenin's Theorem
Thevenin's Theorem replaces a complex linear network with an equivalent voltage source (Vth) in series with an equivalent impedance (Zth).
Question 4: Two resistors of 6 Ω and 12 Ω are connected in parallel. What is their combined equivalent resistance?
- 18 Ω
- 9 Ω
- 4 Ω (Correct answer)
- 2 Ω
Correct answer: 4 Ω
For parallel resistors: 1/Req = 1/6 + 1/12 = 3/12, so Req = 4 Ω.
Question 5: The time constant of an RL circuit is defined as the time for the current to reach what percentage of its final steady-state value?
- 50%
- 63.2% (Correct answer)
- 86.5%
- 99%
Correct answer: 63.2%
One time constant (τ = L/R) is the time for current to reach approximately 63.2% of its final steady-state value.
Question 6: In a purely capacitive AC circuit, the current leads the voltage by how many degrees?
- 0°
- 45°
- 90° (Correct answer)
- 180°
Correct answer: 90°
In a purely capacitive circuit, current leads voltage by 90° because the capacitor charges in response to applied voltage.
Question 7: What is the power factor of a purely inductive circuit?
- 1
- 0.707
- 0.5
- 0 (Correct answer)
Correct answer: 0
A purely inductive circuit has a power factor of 0 because the voltage and current are 90° out of phase, resulting in no real power consumed.
EETC Circuit Theory 2
In a series RLC circuit at resonance, what is the relationship between inductive reactance (XL) and capacitive reactance (XC)?