Here are the top 50 commonly asked questions in Electric Circuits interviews. Whether you’re just starting your preparation or need a quick refresher, these questions and answers will help you tackle your interview with confidence.
Basic Electric Circuits Interview Questions with Answers
1. What are the limitations of ohm’s law in Electric Circuit Theory?
The limitations of Ohm’s law are that it does not apply to unilateral networks and non-linear elements. This law gives the relation between voltage and current only when the physical conditions and temperature of the conductor are constant.
2. What is a tree of a graph in Electric Circuit Theory?
A tree is a sub-graph of a network that consists of all the nodes of the original graph but does not contain any closed paths. The number of branches in a tree is one less than the number of branches in the original graph.
3. What is the difference between mesh and loop in Electric Circuit Theory?
A closed path through a circuit, where a node is not encountered more than once is called a loop while a closed path in a circuit with no other circuit paths inside, is called a mesh. A mesh is a loop but a loop is not always a mesh.
4. What is the condition for maximum power transfer in Electric Circuit Theory?
The condition for maximum power transfer in a circuit is that the load resistance must be equal to the source resistance for a purely resistive circuit and the load impedance must be equal to the conjugate of source impedance for other circuits.
5. What is the RMS value of periodic current in Electric Circuit Theory?
The RMS value of periodic current is the dc current that can deliver the same average power to a resistor as the periodic current. RMS value gives the heating effect of the waveform.
6. What is the power factor for resistive and reactive circuits in Electric Circuit Theory?
The power factor for a purely resistive circuit is 1 and for purely reactive circuits is zero. The power factor lies between 0 and 1 for circuits with a combination of resistive and reactive elements.
7. What is the coefficient of coupling in Electric Circuit Theory?
Coefficient of coupling, K indicates the amount of coupling between two inductively coupled coils with mutual inductance, M, and self-inductance L1 and L2.
K = M\(\sqrt{L_1 L_2}\)
8. What is mutual inductance in Electric Circuit Theory?
Mutual inductance between two coupled coils is the ratio of flux linkage in one coil due to its common flux to the current through the other coil, when the permeability is constant.
9. What is zero input response in Electric Circuit Theory?
The zero input response is the response of the circuit obtained when the input is zero. Due to the initial charge on the capacitor and initial flux on the inductor, there may be a finite response even if the input is zero.
10. What is the time constant of the RL series circuit in Electric Circuit Theory?
The time in which the current rises to 63.2% of its steady-state value is the time constant of the RL series circuit.
τ=\(\frac{L}{R}\)
11. When does resonance condition occur in Network Theory?
A resonance condition in an RLC circuit occurs when the capacitive and inductive inductances are equal in magnitude. Such a circuit results in a purely resistive circuit.
12. What is the quality factor in Network Theory?
Quality factor gives a relationship between the peak energy stored in the circuit to the energy dissipated in the circuit per cycle at resonance.
Q=2π \(\frac{Peak \, energy \, stored \, in \, the \, circuit}{Energy \, dissipated \, in \, the \, circuit \, per \, cycle}\)
13. What are the situations in which an unbalanced system occurs in Electric Circuit Theory?
The unbalanced system occurs in the following situations:
- When the source voltages are not equal in magnitude or differ in phase.
- When load impedances are unequal.
14. What is the relation between line and phase values in star connection in Electric Circuit Theory?
The relation between line and phase values in star connection are:-
- Voltage relation: EL=\(\sqrt{3} E_{ph}\)
- Current relation: IL=Iph
15. When is a two-port network considered a reciprocal network in Network Theory?
A two-port network is considered a reciprocal if the voltage appearing at the first port due to a current applied at the second port is the same as the voltage appearing at the second port when the same current is applied to the first port.
16. What is the condition for symmetry and reciprocity for h parameters in Network Theory?
The condition for symmetry and reciprocity for h parameters are:-
- Condition for symmetry: h11 h22-h12 h21=1
- Condition for reciprocity: h12=-h21
17. What is the attenuation constant in Network Theory?
Attenuation constant is the measure of change in magnitude of current or voltage in a network. Attenuation constant is the real part of the propagation constant and is represented as α.
18. What condition must a constant-k type filter satisfy in Network Theory?
Constant-k type filters satisfy the condition [Z1 Z2=k2] where Z1 and Z2 impedances in T or π are type networks and k is the nominal impedance of the filter.
19. What is the form factor and its value for a sinusoidal wave in Electric Circuit Theory?
Form factor is the ratio of the rms value of a waveform to the average value of the waveform. The form factor of the sinusoidal wave is 1.11.
Form factor = \(\frac{V_{rms}}{V_{avg}}\)
20. What are unilateral elements in Electric Circuit Theory?
Unilateral elements are those elements whose voltage-current relation is different with current flowing in either direction. The polarity of the voltage affects the voltage-current relation of the element. Examples are diodes, metal rectifiers.
Intermediate Electric Circuits Interview Questions with Answers
21. What are passive elements?
The elements that are not capable of generating electrical energy and only can receive power from external devices is a passive element. They cannot deliver average power greater than zero over an infinite time interval. Examples are resistors, capacitors.
22. What is Kirchhoff’s Voltage Law?
Kirchhoff’s Voltage Law commonly referred to as KVL states that the sum of voltage drops in a circuit is equal to the sum of voltage rise in the circuit. KVL is based on the law of conservation of energy.
23. What is the difference between super-mesh and super-node?
A super-node is formed when a voltage source is connected between two non-reference nodes and some other element is connected parallel to it while a super-mesh is formed when two meshes have a current source in common.
24. What is Source Transformation Technique?
Using the Source transformation technique, a practical voltage source can be replaced by a current source in parallel with a resistor, and a practical current source can be replaced by a voltage source in series with a resistor.
25. What is the Reciprocity theorem?
Reciprocity theorem states that in a linear, bilateral single source circuit the ratio of excitation to the response is constant even after the position of excitation and response are interchanged.
26. What is the Thevenin theorem?
Thevenin theorem states that a two-terminal linear network with several sources and resistances, can be replaced with an equivalent circuit with a single voltage source in series with a resistor.
27. What are the limitations of the superposition theorem?
The limitations of the superposition theorem are that it is only valid for linear systems. This theorem can only be used to calculate the current flowing through or voltage across an element but cannot be used for calculating power absorbed or dissipated.
28. What is the Compensation theorem?
Compensation theorem states that a linear element in a bilateral network can be replaced by a voltage source of magnitude equal to the product of current passing and the value of the element when currents and voltages in other parts remain unaltered.
29. What are the dual of a voltage source and a series circuit?
The dual of a voltage source is a current source and the dual of a series circuit is a parallel circuit.
30. What is the average value of a sinusoidal wave?
Average value of a wave is the total area under the wave divided by the total distance of the wave. The average value of a sinusoidal wave over a complete cycle is 0.
Vavg = \(\frac{1}{T} ∫_0^T v(t)dt \)
31. What is the peak factor and its value for a sinusoidal wave?
The peak factor is the ratio of the peak value of a waveform to the rms value of the waveform. The form factor of the sinusoidal wave is 1.414.
Peak factor = \(\frac{V_{peak}}{V_{rms}}\)
32. How does the current change when the frequency of voltage across a capacitor is increased?
The current in the circuit increases when the frequency of voltage across a capacitor is increased. This is because the current will be directly proportional to the frequency when a constant voltage is given.
I=(jωC)V
33. What are the magnitude of impedance and the phase angle in a series RLC circuit?
The magnitude of impedance and the phase angle in a series RLC circuit are:-
- Magnitude of impedance: Z = \(\sqrt{R^2 + (X_L-X_C)^2}\)
- Phase angle: θ=tan-1 \(\frac{X_L-X_C}{R}\)
34. What is the self-inductance of a coil?
The self-inductance of a coil is the ratio of flux linkage to the current through the coil when the permeability is constant.
L= N \(\frac{∅}{I}\)
35. What is the expression for equivalent inductance of two inductively coupled coils connected in series?
The expression for equivalent inductance of two inductively coupled coils connected in series are:
L= L1+L2±2M
Where, L1 and L2 represent the self-inductances and M represents the mutual inductance. A positive sign is for series aiding and a negative sign is for series opposing.
36. What is the expression for equivalent inductance of two inductively coupled coils connected in parallel?
The expression for equivalent inductance of two inductively coupled coils connected in parallel is
L = \(\frac{L_1 L_2-M^2}{L_1+L_2∓2M}\)
Where, L1 and L2 represent the self-inductances and M represents the mutual inductance. A positive sign is for parallel opposing and a negative sign is for parallel aiding.
37. What is the zero state response of a circuit?
The zero state response is the response of the circuit obtained for an arbitrary input when all the initial conditions are is zero.
38. What is the time constant of the RC series circuit?
The time in which the current falls to 36.8% of its initial current is the time constant of the RC series circuit.
τ=RC
39. Why is a natural response called a transient response?
The internal energy stored in the network determines the natural response. The natural response is called transient response because such a response dies out as time approaches infinity.
40. How does an inductor act at t=0+ and t=∞?
The inductor with no initial current acts as an open circuit at t=0+, as the current flowing in an inductor cannot change instantaneously. The inductor at t=∞ acts as a short circuit.
41. How does a capacitor act at t=0+ and t=∞?
The capacitor with no initial voltage acts as a short circuit at t=0+, as the charge in a capacitor cannot change instantaneously. The capacitor at t=∞ acts as an open circuit.
42. What is the condition at which the response of the RLC series circuit is underdamped for a step input?
RLC series circuit is underdamped for a step input when:
\( (\frac{R}{2L})^2 \ge \frac{1}{LC}\)43. What is the resonant frequency in an RLC circuit?
The resonant frequency in an RLC circuit is the inverse of the square root of the product of capacitance and inductance.
ωo = \(\frac{1}{\sqrt{LC}}\)
44. What is the relation between quality factor and bandwidth?
The quality factor of a resonant circuit can be referred to as the ratio of resonant frequency to its bandwidth. A higher value of Q gives smaller bandwidth whereas a lower value of Q gives larger bandwidth.
Q = ωo/B
45. What is selectivity in an RLC circuit?
Selectivity is the ability of the RLC circuit to respond to a certain frequency and discriminate against all other frequencies. Selectivity is high for a circuit with narrow bandwidth while selectivity is low for a circuit with large bandwidth.
46. What are the line and phase values in delta connection?
The relation between line and phase values in delta connection are:-
- Voltage relation : EL=Eph
- Current relation : IL= \(\sqrt{3} I_{ph}\)
47. What is the value of neutral current in a three-phase unbalanced, four-wire star connected system?
The value of neutral current in a three-phase unbalanced, four-wire star connected system is equal to the vector sum of currents in the three lines.
48. When is a two-port network considered a symmetrical network?
A two-port network is considered to be symmetrical if the ratio of the excitation to the response remains the same at first as well as the second port for the circuit parameters.
49. What is the condition for symmetry and reciprocity for transmission parameters?
The condition for symmetry and reciprocity for transmission parameters are:-
Condition for symmetry: A=D
Condition for reciprocity: AD-BC=1
50. Why are Z parameters called the open-circuit impedance parameters?
The Z parameters are called open circuit impedance parameters because these correspond to the impedance when one of the ports is open-circuited.
51. What is the phase shift constant in a complex function?
Phase shift constant is the difference in phase between the input or output current or voltage in a network. This is the imaginary part of the propagation constant and is represented as β.
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