Network Theory: Important interview questions Part-2

1. State the advantages offered by graph theory as applied to electric circuit problems?

Ans.

1. Graph theory or network topology deals with those properties of network which do not change with the change in the shape of the networks.
2. All the equations (KCL and KVL) formed by graph theory concept are independent equations.
3. The graph-theory concept eases the solution method for solving networks with a large number of nodes and branches.

2. Mention some examples where the reciprocity theorem is not applicable?

Ans:

1. This theorem is inapplicable to unilateral networks comprising of elector tubes or other control devices.
2. This theorem is inapplicable to circuits with time-varying elements.
3. This theorem is inapplicable to circuits with dependent sources.
4. To apply this theorem, we have to consider only the zero-state response by taking all the initial conditions to be zero.

3. Mention some limitations of the Online Classroom Program position's theorem.

Ans.

This theorem is not valid for power relationship.

This theorem is not applicable to circuits containing only dependent sources. With dependent sources, superposition can be used only when the controlling functions are external to the network-containing sources, so that the controls are unchanged when the sources act at a time.

4. What is the use of superposition theorem?

Ans. The superposition theorem is used to find the current or voltage in a branch when the circuit has a large number of independent voltage and/or current sources.

5. Mention some examples where the Thevenin's theorem cannot be applied? (IES-06)

Ans.

• This theorem is inapplicable to loads which are magnetically coupled to other parts of the circuit.
• This theorem is inapplicable for non-linear and unilateral networks.
• To apply this theorem, the load should not contain any dependent source.

6. Explain the application and limitations of Milliman's theorem. (IES-06)

Ans.

• This theorem provides the equivalent circuits which are either Thevenin's or Norton Equivalent circuits.
• This theorem is applicable only their independent voltage sources with their internal series impedances connected directly in parallel, or independent current sources with their internal series admittances connected directly in series.

Limitations:

• This theorem is not applicable to circuits where impedances or dependent sources are present between the independent sources.
• This theorem is not useful for circuits with less than two independent sources.

7. Discuss the advantage of the Laplace Transform method over the conventional classical methods of solving the linear differential equations with constant coefficients? (IES-06)

Ans: Advantages of Laplace Transform Method:

• It gives a complete solution.
• Initial conditions are automatically considered in the transformed equations.
• Much less time is involved in solving differential equations.
• It gives systematic and routing solutions for differential equations.

8. Why the ABCD parameters termed 'transmission parameters'?  (IES-10)

Ans. The ABCD parameters represent the relation between the input quantities and the output quantities in a two-port network.

They are thus voltage-current pairs.

These parameters are known as transmission parameters as  in a transmission line, the currents enter at one end and leave at the other end, and we need to know a relation between the sending-end quantities and the receiving-end quantities.

9. What is a gyrator? Mention some properties of an ideal gyrator. Show that a gyrator is a non reciprocal device.

Ans:

A gyrator is a two-port network that is designed to transform load impedance into an input impedance where the input impedance where the input impedance is proportional to the inverse of the load impedance. It is characterized by a single resistance R, known as the gyration resistance.

Properties of a gyrator:

• A gyrator is a non-energic or passive element, i.e, at all times the power delivered to the two-part is identically zero.
• When a gyrator is terminated at the output port with a linear resistance R_L, the input port behaves as a linear resistor with resistance

• If the output port of an ideal gyrator is terminated with a capacitor, the input port behaves like an inductor.
• If the output of an ideal gyrator is terminated with an inductor, the input port behaves like a capacitor.

10. What is negative impedance converter (NIC)?

Ans. A negative impedance converter (NIC) is a two port device that offers negative impedance, i.e., the impedance seen at the input is equal to the negative of the load impedance with some conversion ration.

11. Explain active and reactive power. What is the physical significance of reactive power? (IES-13)

Ans:

1. Active power: It is the average of the instantaneous power over a time interval. It is the power consumed by the resistive loads in an electrical circuit.

In sinusoidally steady state, the active power is given as

1. Reactive power: It is defined as the product of the applied voltage and reactive component of the current. It expressed as volt-ampere reactive (VAR).

For an ac load with voltage phasor V = V_m ∠θ_V, and current phasor I = I_m ∠θ_i, the reactive power is written as

Q = V _rms I _rms sin (θ_v — θ_i)   

12. what is power triangle?

Ans. The relationship between real power, reactive power and apparent power can be expressed by representing the quantities as vectors. Real power is represented as a horizontal vector and reactive power is represented as a vertical vector. The apparent power vector is the hypotenuse of a right angle triangle formed by connecting the real and reactive power vectors. This representation called the power triangle.

13. Explain the concept of Mutual inductance?

Ans. When two coils are placed very close to each other, the magnetic flux caused by the current in one coil links with the other coil and induces some voltage in the second coil. This phenomenon is known as mutual inductance.

14. Explain the consequences of phase reversal of a three-phase unbalanced delta-connected load?

Ans:

• Phase currents remain the same in magnitude, but their phase angles are changed.
• Line currents change both in magnitude and phase.

15. The series resonant circuit is often regarded as the acceptor circuit and the parallel resonant as the rejector circuit. Explain?

Ans. In the case of series resonance, the impedance at the resonant frequency is the minimum so that the current in the series circuit becomes the maximum. On the other hand, in case of parallel resonance, the impedance at the resonant frequency is the maximum so that current in the series circuit becomes the minimum.

Therefore series resonance circuit is termed as accepter circuit and parallel resonance circuit is regarded as rejecter circuit.

16. At resonance, the current is maximum in a series circuit why?

Ans. In a series circuit, at resonance, the inductive and capacitive reactance's cancel each other and the impedance is minimum and equal to the resistance of the circuit. Hence in a series resonant circuit, the current will be maximum.

17. The shape of the resonance curve depends on Q of the coil. Why?

Ans. The bandwidth of a series RLC circuit, defined as, Bandwidth = ,depends upon the Q of the coil. A circuit will be highly selective (narrow bandwidth) if it has a high value of Q. for a series RLC circuit, a high value of the quality factor implies a narrow resonant peak and a low value of Q implies a broad resonant peak.

You Can Check the following link for a complete set of interview questions : 

Brush up your Concepts with 1000+ Important Interview Questions

Thanks

The Most Comprehensive Exam Prep App. Stay Safe!