NETWORK THEORY INTERVIEW QUESTIONS AND ANSWERS
Q.1. What will be the effect of using capacitor for power factor correction in a single phase circuit?
Answer: A capacitor used for power factor correction in single-phase circuit decreases the line current and increases power factor.
Q3. Comment upon the pole and zero of voltage transfer function of a simple RC integrator?
Answer: Voltage transfer function of a simple RC integrator has a zero at infinity and a finite pole.
Q.4. A 10 ohm resistor, a 1H inductor and 1 micro farad capacitor are connected in parallel. The combination is driven by a unit step current. Under the steady state condition, the source current flow through which element?
Answer: At steady state inductor behaves as short circuit. So, under steady state condition the source current flows through the inductor.
Q.5. What is the necessary and sufficient condition for a rational function of s, T(s) to be a driving point impedance of an RC network?
Answer: The necessary and sufficient condition is that all poles and zeros should be simple and lie on the negative real axis of the s-plane. The poles and zeros of the ZRC(s) should be simple and alternates on the negative real axis of the s-plane.
Q.6. What are the properties of RL driving point impedance?
Answer: The properties of RL driving point impedance are as follows-
- Poles and zeros lie on the negative real axis.
- Poles and zeros are alternate on negative real axis.
- The entity nearest to origin is a zero and that nearest to infinity is a pole.
- Residues must be positive.
- The slope of the curve is positive at all points.
Q.7. What is the value of internal admittance of an ideal current source?
Answer: The internal impedance of an ideal current source is infinite. In other words, the internal admittance of an ideal current source is zero.
Q.8. What should be the condition between applied signal frequency and resonant frequency for overall reactance to be inductive and capacitive?
Answer: When applied frequency is less than resonant frequency than the overall reactance will be capacitive.
When applied frequency is greater than resonant frequency than the overall reactance will be inductive.
Q.9. When it is convenient to use ABCD, Z and Y parameters?
Answer: When two networks are connected in cascade then it is convenient to use ABCD parameters.
When two networks are connected in series then it is convenient to use z parameters.
When two networks are connected in parallel then it is convenient to use Y parameters.
Q.10. What is image impedance of the network?
Answer: If two impedance Zi1 and Zi2 are such that Zi1 is driving point impedance at port 1 with Zi2 connected to port 2 and Zi2 is driving point impedance at port 2 with Zi1 connected to port 1 then Zi1 and Zi2 are called image impedance of the network.
Q.11. What is magnetic coupling?
Answer: When a portion of magnetic flux established by one circuit interlinks with the second circuit, the two circuits are said to be coupled magnetically and energy may be transferred from one circuit to other through the medium of magnetic flux which is common to both.
Q.12. What is the difference between Apparent power and Reactive power?
Answer: Apparent Power- The product VI is called the apparent power and it is usually indicated by the symbol ‘S’. It is expressed in VA.
Reactive Power- The product of rms value of current and voltage and sine of the angle between them is called reactive power. It is denoted by ‘Q’ and is expressed in VAR.
Q.13. Is it possible to obtain transient free response in RLC circuit?
Answer: In RLC circuit it is not possible to obtain transient free response, since circuit is having two independent energy storage elements Land C.
Q.14. Where the study of resonance is very useful?
Answer: The study of resonance is very useful in the area of communication particularly. For example, the ability of a radio receiver to select a certain frequency transmitted by a station and to eliminate frequencies from other stations is based on the principle of resonance.
Q.15. What is the condition for maximum power transfer to take place?
Answer: For maximum power transfer to take place the resistance of the load should be equal to the source resistance and the reactance of the load should be equal to that of source in magnitude but opposite in sign. It means, if load is capacitive then source is inductive and vice-versa.
Q.16. Explain the switching action of an inductor?
Answer: The current through an inductor cannot change instantaneously. If an energy source is suddenly connected to an inductor then it will not cause current to flow initially. Thus inductor acts as open circuit for the new applied source at the instant of switching.
If a current of vale IO flows in the inductor at the instant switching takes place, that current will continue to flow. For the initial instant, the inductor may be considered as a current source of current IO.
Q.17. Define current, voltage and power.
Answer: The time rate of flow of electric charge across a cross-sectional boundary is termed as current.
Voltage is defined as work done in moving a unit positive charge once around the closed path.
The instantaneous power delivered to circuit elements is the product of the instantaneous value of voltage and current of the element. In terms of energy, power is defined as “The time rate of change of energy is called power”.
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