This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Frequency Variation in a Series RLC Circuit”.

1. If the resonant frequency in a series RLC circuit is 50kHz along with a bandwidth of 1kHz, find the quality factor.

a) 5

b) 50

c) 100

d) 500

View Answer

Explanation: We know that Quality factor is equal to the resonant frequency divided by the bandwidth.

Q=f

_{res}/Bandwidth = 50/1 = 50.

2. What is the SI unit for quality factor?

a) Hz

b) kHz

c) MHz

d) No unit

View Answer

Explanation: We know that Quality factor is equal to the resonant frequency divided by the bandwidth. It is one frequency divided by another hence it has no unit.

3. What happens to the quality factor when the bandwidth increases?

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

View Answer

Explanation: Q=f

_{res}/Bandwidth

Quality factor is inversely proportional to bandwidth. So, if bandwidth increases quality factor decreases.

4. What happens to the quality factor when resonant frequency increases?

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

View Answer

Explanation: Q=f

_{res}/Bandwidth

Quality factor is directly proportional to resonant frequency. So, if resonant frequency increases quality factor increases.

5. Resonance frequency occurs when __________________

a) X_{L}=X_{C}

b) X_{L}>X_{C}

c) X_{L}<X_{C}

d) Cannot be determined

View Answer

Explanation: The frequency of a system is said to be resonating when the value of the capacitive reactance and the inductive reactance is the same.

6. The current leads the supply voltage in a series RLC circuit has its frequency _________ the resonant frequency.

a) Above

b) Below

c) Equal to

d) Cannot be determined

View Answer

Explanation: Current is leading the voltage indicates capacitor dominating circuit. X

_{C}>X

_{L}=> 1/(ωC) > ωL => ω<1/√LC

So, frequency less than resonant frequency.

7. What is the power factor of a series RLC circuit under resonance condition?

a) 0

b) 1

c) Infinity

d) 100

View Answer

Explanation: The power factor for a series RLC circuit in resonance condition is always unity because the current is in phase with the voltage under resonance condition.

Φ=0

^{0}=> cos ϕ = 1 i.e. power factor = 1.

8. The current lags the supply voltage in a series RLC circuit has its frequency _________ the resonant frequency.

a) Above

b) Below

c) Equal to

d) Cannot be determined

View Answer

Explanation: Current is lagging the voltage indicates inductor dominating circuit. X

_{C}< X

_{L}=> 1/(ωC) < ωL => ω > 1/√LC

So, frequency more than resonant frequency.

9. What is the correct formula for quality factor?

a) Q=BW*fr

b) Q=BW/fr

c) Q=fr/BW

d) Q=fr2

View Answer

Explanation: The correct formula for quality factor is Q=fr/BW, where fr is the resonant frequency, BW is the bandwidth frequency and Q is the quality factor.

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