Microwave Engineering Questions and Answers – Series and Parallel Resonant Circuits

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Series and Parallel Resonant Circuits”.

1. In a series LCR circuit, at resonance point the energy stored in the inductor and capacitor in the form of magnetic and electric energies are equal.
a) True
b) False
View Answer

Answer: b
Explanation: At resonant frequency of a series LCR circuit, reactance of the capacitor is equal to the reactance of the inductor. The energy stored in the capacitor in the form of electric energy and the energy stored in the inductor in the form of magnetic energy is both equal.

2. Quality factor-Q of a resonant circuit signifies:
a) Loss in the resonant circuit
b) Gain in the resonant circuit
c) Magnetic energy stored in the circuit
d) Electric energy stored in the circuit
View Answer

Answer: a
Explanation: Quality factor of a resonant network is defined as the ratio of average energy stored to the energy loss/ second. Hence, lower loss implies a higher quality factor.

3. The total energy stored in a series RLC circuit is equal to the energy stored in the inductor.
a) True
b) False
View Answer

Answer: b
Explanation: The total energy in an RLC circuit is the sum of the energy stored in the magnetic field of the inductor and the electric energy stored in the capacitor. Loss in the circuit occurs due to the resistive component.
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4. Higher the quality factor of a series LCR circuit, greater is the operating bandwidth of the resonant circuit.
a) True
b) False
View Answer

Answer: b
Explanation: Band width and quality factor of a series RLC circuit are both inversely related. Higher the quality factor, lower the operating bandwidth.

5. The plot of input impedance magnitude v/s frequency has a peak at the resonant frequency.
a) True
b) False
View Answer

Answer: b
Explanation: At resonant frequency, the capacitive reactance is equal to the inductive reactance cancelling each other’s effect. Hence, there is a dip at the center frequency in the plot of input impedance magnitude v/s frequency.

6. For a parallel resonance circuit, the plot of input impedance magnitude v/s frequency has a dip at the resonant frequency.
a) True
b) False
View Answer

Answer: b
Explanation: In parallel RLC circuit, the input impedance is highest at resonant frequency since the reactive components are in parallel. Hence, there is a peak at the resonant frequency in the plot of input impedance magnitude v/s frequency.

7. The relation between unloaded Q and external Q is:
a) External Q> unloaded Q
b) Unloaded Q> external Q
c) External Q = unloaded Q
d) None of the mentioned
View Answer

Answer: b
Explanation: To compute unloaded Q only the resistance in the resonant circuit is considered. But to calculate external Q, the resistance and other load in the external load is also considered. Sine Q and R are inversely proportional, as R increases Q decreases. Since R is greater for external Q computation, unloaded Q> external Q.
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8. Loaded Q and External Q are 2 different parameters.
a) True
b) False
View Answer

Answer: a
Explanation: loaded Q and external Q are 2 different parameters. They are related by the expression
QL-1=Qe-1+ Q0-1, where QL is the loaded Q, Qe is external Q and Q0 is the unloaded Q.

9. The bandwidth of a series RLC circuit is 200 Hz. Then the quality factor of the circuit is:
a) 200
b) 100
c) 0.005
d) 0.5
View Answer

Answer: c
Explanation: The relation between quality factor and bandwidth is given as bandwidth=Q-1. Substituting for bandwidth in this expression, the quality factor of the resonant circuit is 0.005.
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10. If a parallel RLC circuit is excited with a source of 8v, 50 Hz and the circuit has an inductor of 1mH, capacitor of 1µF and a resistor of 50Ω, then the power loss that occurs in the circuit is:
a) 6.4mW
b) 3.2mW
c) 12.8mV
d) None of the mentioned
View Answer

Answer: a
Explanation: The power loss in a parallel RLC circuit is 0.5│V│2/R. given the values of source voltage and resistance in the circuit, the power loss in the parallel RLC circuit is 6.4mW.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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