30 TOP Circuit Design Engineer Interview Questions and Answers pdf free download

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1. The Numerical Values Of What Circuit Elements Are Typically Represented Using Colored Stripes?
The numerical values of resistors circuit elements are typically represented using colored stripes.

2. Which Of These Statements Expresses De Morgan's Theorem?
NOT (A AND B) = (NOT A) OR (NOT B)

3. In A Low-pass Filter Consisting Of A Resistor And A Capacitor, How Will The Cut-off Frequency Change If The Capacitance Is Increased?
The cut-off frequency is lower for larger capacitances.

Circuit Design Engineer Questions & Answers

4. In A High-pass Filter Consisting Of A Resistor And A Capacitor, How Will The Cut-off Frequency Change If The Capacitance Is Increased?
The cut-off frequency is lower for larger capacitances.

5. A High-voltage Primary Circuit Is Isolated With The Use Of An Optocoupler On A Secondary Circuit. Does The Addition Of The Optocoupler Add Inductance To Either Circuit?
no, the optocoupler does not add inductance.

6. Consider A Switch On A High-voltage Circuit That Is Unsafe To Operate Manually. How Might The Switch Be Safely Actuated?
by using a secondary, low-voltage relay circuit.

7. To What Does The "sample Rate" Of A Signal Refer?
how often in time the signal is sampled.

8. Which Model Is Generally Used For Transmission Lines?
distributed element model is generally used for transmission lines.

9. How To Use Breadboard?
Breadboard used as a construction base for prototyping of a circuit.

10. How Does The Breakdown Voltage Of A Dielectric Depend Upon Its Thickness?
a thick layer of dielectric has a higher breakdown voltage than a thinner layer of the same dielectric.

11. If In A Circuit The Input Voltage (vin) Is Applied Across The Series Impedances Z1 And Z2 And The Output Is Taken Across Z2, What Is The Output Voltage (vout) Given By?
[Z2 / (Z1 + Z2)] . Vin

12. A String Of Decorative Holiday Lights Are Lit Except For Two Burnt-out Bulbs. Are The Bulbs Of The String Wired In Parallel Or Series With Each Other?
The lights must be wired in parallel with each other.

13. How Many Diodes Are Required To Build The Bridge In A Full-wave Rectifier That Does Not Employ A Transformer?
four diodes are required to build the bridge in a full-wave rectifier that does not employ a transformer.

14. According To Kirchhoff's Voltage Law, The Sum Of The Emfs In Any Closed Loop Is Equal To?
The sum of the potential drops in that loop.

15. What Are The Names Of The Three Terminals On A Bjt Transistor?
base
collector
emitter

16. Which Is A Primary Disadvantage Of A Solid-state Amplifier Compared With A Vacuum-tube Amplifier?
poor tolerance for high -current and -voltage transients.

17. How Is The Nyquist Rate For A Signal Related To The Bandwidth Of The Signal?
a wider bandwidth requires a higher Nyquist rate.

18. What Is The Approximate Impedance Of A Universal Serial Bus (usb) Computer Connection?
50 Ohm

19. What Is The Function Of A Diode Clamp?
to maintain the voltage of a signal between fixed bounds.

20. To What Do The "rails" Of An Operational Amplifier Refer?
the potentials of the positive and negative terminals of the power supply.

21. In A Differentiator Circuit, The Output Is Approximately?
directly proportional to the rate of change of input.

22. One 50-ohm Resistor And Two Parallel 100-ohm Resistors Have The Same Impedance. In Which System Do The Resistors Have Lower Current When Dissipating 1 Kw?
the system with two 100-Ohm resistors.

23. On A Printed Circuit Board That Supports Several Different Inductors In Different Circuits, Are There Any Constraints To The Layout Of The Inductors?
Yes, the inductors must be oriented at right angles in order to avoid coupling.

24. On A Printed Circuit Board, What Is A Flux Capacitor?
An exploitation of the capacitance that is due to the lateral electric flux between two adjacent printed conductors.

25. What Is The Characteristic Feature Of Heterodyne Processing Compared With Homodyne Processing?
only heterodyne processing employs frequency conversion.

26. The Self-induced Back Voltage In A Circuit That Occurs When An Inductive Dc Circuit Is Opened May Be Safely Routed Away From The Switch With A Diode Connected Across The Inductor And Against The Dc Voltage. What Is The Main Disadvantage Of This Practice?
the decay of the current in the inductor is relatively slow.

27. Why Does An "l Pad" Impedance-matching Network Bear That Name?
Because the two resistors in the network are traditionally oriented in the shape of the capital letter "L" on schematic drawings.

28. In A High-pass Filter Consisting Of A Resistor And An Inductor, How Will The Cut-off Frequency Change If The Inductance Is Increased?
The cut-off frequency is lower for larger inductances.

29. Dithering Of An Audiofrequency Signal Typically Occurs At What Stage?
following digital-to-analog conversion and prior to playback.

30. Which Of The Following Statements Can Be Made Concerning A Xnor (b Xnor C) = (a Xnor B) Xnor C ?
this is true because XNOR is associative.

Latest Circuit Design Engineer Interview Questions for freshers and Experienced pdf

50 TOP Electrical Circuits Interview Questions and Answers pdf download

Real Time Electrical Circuits Interview Questions with Answers PDF

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1. What id difference between power and energy?
Answer: Energy is defined as the capacity of a physical system to perform work. In the context of electric circuits, energy (w) is related to power by the following relationship p = vi =dw/dt
So the difference is that power is the rate of change of energy.

2. What do you mean by Phasors?
Answer: Addition of two out-of-phase sinusoidal signals is rather complicated in the time domain. An example could be the sum of voltages across a series connection of a resistor and an inductor. Phasors simplify this analysis by considering only the amplitude and phase components of the sine wave. Moreover, they can be solved using complex algebra or treated vectorially using a vector diagram.

3. What is Corkscrew Rule?
Answer: As current flows along a wire, the magnetic field rotates in the direction of a corkscrew.

Electrical Circuits Questions & Answers

4. Differentiate between Kirchhoff’s First law and Kirchhoff’s Second law?
Answer:
Kirchhoff’s First law: The total current leaving a point on an electrical circuit = total current entering
Kirchhoff’s Second law: The sum of the voltages round any circuit = net “IR” drop in the circuit

5. How to calculate Energy stored in an inductance?
Answer: Energy stored =½ L I2 Joules, where L is in henries and I is in amps

6.What is a capacitor and what does it do?
Answer: Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.

7. What is Current Divider Rule (CDR)?
Answer: Current divider rule provides a useful relationship for determining the current through individual circuit elements that are connected in parallel.

8. What is Voltage Divider Rule?
Answer: Voltage divider rule provides a useful formula to determine the voltage across any resistor when two or more resistors are connected in series with a voltage source.

9. What is Current?
Answer: Current can be defined as the motion of charge through a conducting material. The unit of current is Ampere whilst charge is measured in Coulombs.

10. Could you measure Voltage in series?
Answer: No, Voltage is always measured across (in parallel with) a circuit element.


11. What is Kirchoff’s Current Law (KCL)?
Answer: The algebraic sum of all the currents entering or leaving a node in an electric circuit is equal to zero. In other words, the sum of currents entering is equal to the sum of currents leaving the node in an electric circuit.

12. Define Super node?
Answer: A super node exists when an ideal voltage source appears between any two nodes of an electric circuit. The usual way to solve this is to write KCL equations for both nodes and simply add them together into one equation ignoring the voltage source in question. However, this would mean one less equation than the number of variables (node voltages) present in the circuit. A constraint equation can be easily specified given by the magnitude of the ideal voltage source present between the nodes and the respective node voltages. The following example will help clarify this scenario.

13. What does Ampere turns shows?
Answer: mmf A coil of N turns carrying a current I amps gives an mmf of NI ampere turns In a vacuum, a magnetizing force of 1 ampere turn / metre produces a magnetic field of 1.26 × 10-6 tesla.

14. What is the difference between an inductor and a capacitor?
Answer:
An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.
A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates").

15. How does a capacitor store an electrical charge?
Answer: Electrical Energy in Capacitor stores in Potential Charge form. The energy stored in a capacitor is almost entirely in the electric field produced between the plates. It takes energy from a battery or some other power source to move electrons to one of the plates and away from the other.

16: Define Ampere?
Answer: The quantity of total charge that passes through an arbitrary cross-section of a conducting material per unit second is defined as an Ampere.
Mathematically,
I =Q/t
or, Q = It
Where, Q is the symbol of charge measured in Coulombs (C), I is the current in amperes (A) and t is the time in seconds (s).

17: Define Ohm’s Law for A.C (Alternating Current)?
Answer: Everything else would remain same only the resistance will be replaced with Impedance, which is defined as the opposition to the flow of A.C.

18: What do you mean by dependent and independent voltage sources?
Answer: In general, there are two main types of DC sources
Independent (Voltage and Current) Sources
Dependent (Voltage and Current) Sources
An independent source produces its own voltage and current through some chemical reaction and does not depend on any other voltage or current variable in the circuit. The output of a dependent source, on the other hand, is subject to a certain parameter (voltage or current) change in a circuit element. Herein, the discussion shall be confined to independent sources only.

19: Differentiate between Magnetic field and Magnetic Flux?
Answer: Magnetic field is B = µ H where B is in tesla and H = 1.26 × 10-6 times ampere turns/metre MMF in a solenoid of N turns and current I mmf = (4 m / 10) N I Gilberts.
Whereas Magnetic flux f = B A where ø is in weber, B is in tesla and A is in square meters.
Magnetic flux in a uniform closed magnetic circuit, length L meters and cross section A square meters is =1.26NItA × 10-6/ L weber.

20: Differentiate between Induced emf and Self inductance?
Answer: Induced emf, E = - N df/dt where E is in volts, N is number of turns and df/dt is in Wb/sec. This equation is the foundation on which Electrical Engineering is based.
Whereas Self Inductance E = - L dI/dt, where E is in volts, L is inductance in henneries and dI/dt is in amps/sec.
Self inductance of a coil wound on a ring of permeability is L = 1.26 N2 µ A / S × 10-6 Henneries, where N is number of turns, A is cross sectional area in m2 and S meters is the length of the magnetic circuit.
Experimental results for a coil of length S meters, diameter d meters and radial thickness t meters with at core indicate L = 3 d2 N2 / (1.2 d + 3.5 S + 4 t) micro Henneries. (t = 0 for a single layer coil).

21: What is the function of the capacitor?
Answer: A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e. insulator).

22: Could you measure current in parallel?
Answer: No, Current is always measured through (in series with) a circuit element.

23: State and define Ohm’s Law?
Answer: It is the most fundamental law used in circuit analysis. It provides a simple formula describing the voltage-current relationship in a conducting material.
Statement: The voltage or potential difference across a conducting material is directly proportional to the current flowing through the material.
V ? I
V = RI or I =V/R
or R =V/I
Where, the constant of proportionality R is called the resistance or electrical resistance, measured in ohms (O).

24: Briefly explain the purpose of Inductor in an electric circuit?
Answer: An inductor is a piece of conducting wire generally wrapped around a core of a ferromagnetic material. Like capacitors, they are employed as filters as well but the most well known application is their use in AC transformers or power supplies that converts AC voltage levels.

25: What is Superposition Theorem?
Answer: Superposition theorem is extremely useful for analyzing electric circuits that contains two or more active sources. In such cases, the theorem considers each source separately to evaluate the current through or voltage across a component. The resultant is given by the algebraic sum of all currents or voltages caused by each source acting independently. Superposition theorem can be formally stated as follows:
“The current through or voltage across any element in a linear circuit containing several sources is the algebraic sum of the currents or voltages due to each source acting alone, all other sources being removed at that time.”

26: What is Force on a conductor in a magnetic field?
Answer: F = B I L Newtons, where B in tesla, I in amps and L in meters.

27: What is an inductor and what does it do?
Answer: An inductor is a passive electronic component which is capable of storing electrical energy in the form of magnetic energy. Basically, it uses a conductor that is wound into a coil, and when electricity flows into the coil from the left to the right, this will generate a magnetic field in the clockwise direction.

28: At what base you will tell the direction of rotation of DC Motors and Generators?
Answer: Motors obey the left hand rule and generators the right hand rule.

29: What is the difference between Voltages or Potential Difference?
Answer: Voltage or potential difference between two points in an electric circuit is 1V if 1J (Joule) of energy is expended in transferring 1 C of charge between those points.
It is generally represented by the symbol V and measured in volts (V). Note that the symbol and the unit of voltage are both denoted by the same letter; However, it rarely causes any confusion.
The symbol V also signifies a constant voltage (DC) whereas a time-varying (AC) voltage is represented by the symbol v or v (t)

30: What does the term “Voltage Regulation” means?
Answer: Voltage regulation (VR) is an important measure of the quality of a source. It is used to measure the variation in terminal voltage between no load (IL =0, open circuit) and full load (IL = IFL)

31: State and define Norton’s Theorem?
Answer: Thevenin’s equivalent circuit is a practical voltage source. In contrast, Norton’s equivalent circuit is a practical current source. This can be formally stated as:
“Any two-terminal, linear circuit, of resistors and sources, can be replaced by a single current source in parallel with a resistor.”
To determine Norton’s equivalent circuit, Norton current, IN, and Norton resistance, RN , are required. The following steps outline the procedure required:
Remove the load resistance, RL.
IN is the SC current through the load terminals and
RN is the resistance across the load terminals with all sources replaced by their internal resistances. Clearly RN = RTH.

32: What does the term Power Factor shows?
Answer: The term cos f is called the power factor and is an important parameter in determining the amount of actual power dissipated in the load. In practice, power factor is used to specify the characteristics of a load.
For a purely resistive load f = 0 Degree, hence Unity Power Factor
For a capacitive type load I leads V, hence Leading power factor
For an inductive type load I lags V, hence Lagging power factor
Clearly, for a fixed amount of demanded power P, at a constant load voltage V, a higher power factor draws less amount of current and hence low I2R losses in the transmission lines. A purely reactive load where f ? 900 and cos f ? 0 will draw an excessively large amount of current and a power factor correction is required.

33: What is the energy stored in the magnetic field of the inductor?
Answer: The formula for the energy stored in a magnetic field is E = ½ LI 2. The energy stored in a magnetic field is equal to the work needed to produce a current through the inductor. Energy is stored in a magnetic field.

34: What is the function of Capacitor in Electrical Circuits?
Answer: A capacitor is a passive circuit element that has the capacity to store charge in an electric field. It is widely used in electric circuits in the form of a filter.

35: What is DC Current source? Differentiate between ideal and non-ideal current sources
Answer: A current source, unlike the DC voltage source, is not a physical reality. However, it is useful in deriving equivalent circuit models of semiconductor devices such as a transistor. It can also be subdivided into ideal and non-ideal categories.

The Ideal Current Source By definition, an ideal current source that produces a current which is independent of the variations in load. In other words the current supplied by an ideal current source does not change with the load voltage.

Non-Ideal or Practical Current Source The current delivered by a practical current source falls off with an increase in load or load voltage.

36: What does the term Super-mesh means?
Answer: A super-mesh exists when an ideal current source appears between two meshes of an electric circuit. In such a situation, like super-node, mesh equations are written for the meshes involved and added giving a single equation. Again, there would be one less equation than the number of variables (mesh currents) and hence a constraint equation is needed. This would be based on the magnitude of the ideal current source present between the two meshes and their mesh currents.

37: How to calculate Energy stored in a capacitance?
Answer: Energy stored = ½ C V2 Joules, where C is in farads and V in volts

38: How many Types of Circuit Loads are there in a Common Electrical Circuit?
Answer: A load generally refers to a component or a piece of equipment connected to the output of an electric circuit. In its fundamental form, the load is represented by any one or a combination of the following:
Resistor (R)
Inductor (L)
Capacitor (C)
A load can either be of resistive, inductive or capacitive nature or a blend of them. For example, a light bulb is a purely resistive load where as a transformer is both inductive and resistive. A circuit load can also be referred to as a sink since it dissipates energy whereas the voltage or current supply can be termed as a source.

39: Differentiate between ideal and non-ideal voltage sources?
Answer: The Ideal Voltage Source An ideal voltage source which has a terminal voltage which is independent of the variations in load. In other words, for an ideal voltage source, the supply current alters with changes in load but the terminal voltage, VL always remains constant. Non-Ideal or Practical Voltage Source For a practical source, the terminal voltage falls off with an increase in load current.

40: What is the method to solve circuit using Source Transformation?
Answer: In an electric circuit, it is often convenient to have a voltage source rather than a current source (e.g. in mesh analysis) or vice versa. This is made possible using source transformations.
It should be noted that only practical voltage and current sources can be transformed. In other words, a Thevenin’s equivalent circuit is transformed into a Norton’s one or vice versa. The parameters used in the source transformation are given as follows.
Thevenin parameters: VTH, RTH =? RN = RTH, IN = VTH/RTH
Norton parameters: IN, RN =? RTH = RN, VTH = RN IN
Any load resistance, RL will have the same voltage across, and current through it when connected across the terminals of either source.

41: Differentiate between Real and Apparent Power?
Answer: It is important to highlight that in AC circuits, the product of voltage and current yields the apparent power which is measured in volt-amperes or VA
KW which is also written ad Kilo-Watt is the real power that is actually converted to the useful work.
KVAR is also termed as Kilo-Volt Reactive this power is used for magnetic field excitation and flows back and forth between source and load.

42: At what factor Resistance R of a conductor depends?
Answer: R = p L (1 + aT) / A ohms where p is resistivity in ohms per cm cube, L cm is the length, A in cm2 is the cross sectional area, a is temp coefficient and T is the temperature in degrees Celsius.
Several sources give Copper p = 1.7 × 10-6 ohms per cm cube and a = 0.004. At very low Temperatures, the resistance of some materials falls to zero

43: Why Inductors are installed in electrical Circuits?
Answer: An inductor is a piece of conducting wire generally wrapped around a core of a ferromagnetic material. Like capacitors, they are employed as filters as well but the most well known application is their use in AC transformers or power supplies that converts AC voltage levels.

44: What is Maximum Power Transfer Theorem?
Answer: As discussed in the section on Thevenin’s theorem, any DC network of sources and resistances can be replaced by a single voltage source in series with a resistance connected across the load:

The maximum power transfer theorem states that the power delivered to the load is maximum when the load resistance, RL is equal to the internal (source) resistance, Rs of the DC power supply.

In other words, it can be said that the load resistance must match the Thevenin’s resistance for maximum power transfer to take place i.e., (Rs = RTH) = RL
When this occurs, the voltage across the load resistance will be Vs/2 and the power delivered to the load is given by which clearly demonstrates maximum power delivered when Rs = RL. Under this condition, the maximum power will be:

45: What does Bode Plots shows?
Answer: Bode plots are graphical ways to display the behavior of a circuit over a wide range of frequencies. By plotting the amplitude and phase versus the logarithm of frequency, each unit of change on the ? axis is equal to a factor of 10 also called a decade of frequency. Also, there may be a wide distribution in the amplitude response over a specified range of frequencies. The usual way is to plot the amplitude in dB and phase in degrees or radians versus the logarithm of frequency.

46: Elaborate Thevenin’s Theorem?
Answer: Thevenin’s theorem provides a useful tool when solving complex and large electric circuits by reducing them to a single voltage source in series with a resistor. It is particularly advantageous where a single resistor or load in a circuit is subject to change. Formally, the Thevenin’s theorem can be stated as:
“Any two-terminal linear electric circuit consisting of resistors and sources can be replaced by an equivalent circuit containing a single voltage source in series with a resistor connected across the load.”
The following steps outline the procedure to simplify an electric circuit using Thevenin’s theorem where VTH and RTH are the Thevenin’s voltage and Thevenin’s resistance respectively.
Remove the load resistance RL.
VTH is the open circuit (OC) voltage across the load terminals
RTH is the resistance across the load terminals with all sources replaced by their internal resistances.

47: Differentiate between Low Pass, High pass and Band Pass filter?
Answer: Filters form a vital part in electrical networks especially where a particular frequency range is of prime concern. For instance, a radio station is broadcasting a transmission at a frequency of 100 MHz. This means that it is required to design a receiving filter which allows only 100 MHz frequency to pass through whilst other frequencies are filtered out. An ideal filter will attenuate all signals with frequencies less than and greater than 100 MHz thus providing the best channel sound quality without any distortion.

Low Pass Filter: A low pass Filter allows low frequencies to pass through the circuit whereas high frequencies are severely attenuated or blocked.
High Pass Filter: A high pass filter, as the name suggests, allows high frequencies to pass through the circuit whilst low frequencies are attenuated or blocked. The cut­-off point or bandwidth concept is the same as in the low pass filter.
Band Pass Filter: A band pass filter permits a certain band of frequencies to pass through the network which is adjusted by the designer. It is simply an amalgamation of a low pass and a high pass filter.

48: Distinguish between self-induction and mutual induction.
Answer:
Self-Induction
Self-Induction is the characteristic of the coil itself.
When the main current in the coil decreases, the induced current opposes the decay of current in the coil.
When the main current in the coil increases, the induced current opposes the growth of current in the coil.
Mutual induction
Mutual induction is the characteristic of a pair of coils.
When the main current in the coil decreases, induced current developed in the neighboring coil opposes the decay of current in the coil.
When the main current in the coil increases, the induced current developed in the neighboring coil opposes the growth of current in the coil.

Latest Electrical Circuits Interview Questions for freshers and Experienced pdf

110 TOP Circuit Theory Multiple choice Questions with Answers pdf

Real Time Circuit Theory Online Quiz Questions and Answers

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1. A sine wave has a frequency of 50 Hz. Its angular frequency is _______ radian/second.
(a) 100 n
(b) 50 jt
(c) 25 JT
(d) 5 n
Ans: a

2. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15
Ans: c

Circuit Theory Multiple choice Questions

3. The period of a wave is
(a) the same as frequency
(6) time required to complete one cycle
(c) expressed in amperes
(d) none of the above
Ans: b

4. The form factor is the ratio of
(a) peak value to r.m.s. value
(6) r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b

5. The period of a sine wave is 1 / 50 seconds. Its frequency is ______.
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz
Ans: d

6. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to
(a) average voltage
(b) r.m.s. voltage  
(c)     peak voltage
(d) none of the above
Ans: b

7. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
(d) not a sinusoid
Ans: a

8.   The peak value of a sine wave is 200 V. Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a


9. If two sine waves of the same frequency have a phase difference of JT radians, then
(a) both will reach their minimum values at the same instant
(b) both will reach their maximum values at the same instant
(c) when one wave reaches its maxi¬mum value, the other will reach its minimum value
(d) none of the above
Ans: c

10. The voltage of domestic supply is 220V. This figure represents
(a) mean value    
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a

11. Two waves of the same frequency have opposite phase when the phase angle between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b

12. The power consumed in a circuit element will be least when the phase difference between the current and voltage is _____.
(a) 180°
(b) 90°
(c) 60°
(d) 0°
Ans: b

13. The r.m.s. value and mean value is the same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c

14. For the same peak value which of the following wave will 'have the highest r.m.s. value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a

15. For the same peak value, which of the following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a

16. For a sine wave with peak value Imax the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b

17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c

18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c

19. For a sine wave with peak value Emax______8.30. the average value is
(a) 0.636 Emax
(b) 0.707 Emax
(c) 0.434 EWc
(d) lAUEmax
Ans: a

20. For a frequency of 200 Hz, the time period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b

21. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that
(a) both waves must have same frequency
(b) both   waves  must  have identical peak values
(c) both waves must have zero value at the same time
(d) none of the above
Ans: a

22. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c

23. Capacitive reactance is more when
(a)     capacitance is less and frequency of supply is less
(b)     capacitance is less and frequency of supply is more
(c) capacitance is more and frequency of supply is less
(d) capacitance is more and frequency of supply is more
Ans: a

24. In a series resonant circuit, the impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
(d) none of the above
Ans: a

25. Power factor of an electrical circuit is equal to
(a) R/Z
(b) cosine of phase angle difference be-tween current and voltage
(c) kW/kVA
(d) ratio of useful current to total cur¬rent Iw/I
(e) all above
Ans: e

26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the induc¬tive load
(c) far away from the inductive load
(d) any where
Ans: b

27. Poor power factor
(a)     reduces load handling capability of electrical system
(b)     results in more power losses in the electrical system
(c) overloads alternators, transformers and distribution lines
(d) results in more voltage drop in the line
(e) results in all above
Ans: e

28. Capacitors for power factor correction are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d

29. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value
(a) will change the maximum value of current at resonance
(6) will change the resonance frequen¬cy
(c) will change the impedance at resonance frequency
(d) will increase the selectivity of the circuit
Ans: d

30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle
(d) none of the above
Ans: c

31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c

32. Inductance of a coil Varies
(a)     directly as the cross-sectional area of magnetic core
(b)     directly  as  square  of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e

33. All the rules and laws of D.C. circuit also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c

34. Time constant of an inductive circuit
(a) increases with increase of inductance and decrease of resistance
(b) increases with the increase of inductance and the increase of resis¬tance
(c) increases with decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a

35. Power factor of an inductive circuit is usually improved by connecting capacitor to it in
(a) parallel
(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a

36. In a highly capacitive circuit the
(a) apparent power is equal to the actual power
(b) reactive power is more than the apparent power
(c) reactive power is more than the actual power
(d) actual power is more than its reactive power
Ans: c

37. Power factor of the following circuit will be zero
(a) resistance
(b) inductance
(c) capacitance      
(d) both (b) and (c)
Ans: d

38. Power factor of the following circuit will be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c

39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the capacities of generators, lines and transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d

40. The time constant of the capacitance circuit is defined as the time during which voltage
(a) falls to  36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
Ans: c

41. In a loss-free R-L-C circuit the transient current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c

42. The r.m.s. value of alternating current is given by steady (D.C.) current which when flowing through a given circuit for a given time produces
(a) the more heat than produced by A.C. when flowing through the same circuit
(b) the same heat as produced by A.C. when flowing through the same circuit
(c) the less heat than produced by A.C. flowing through the same circuit
(d) none of the above
Ans: b

43. The square waveform of current has following relation between r.m.s. value and average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than average value
(c) r.m.s. value of current is less than average value
(d) none of the above
Ans: a

44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d)     R-L-C circuit
Ans: d

45. The transient currents are associated with the
(a) changes in the stored energy in the inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a

46. The power factor at resonance in R-L- C parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d

47. In the case of an unsymmetrical alternating current the average value must always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d

48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d)     current is in phase with the voltage
Ans: d

49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by 90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b

50. In a circuit containing R, L and C, power loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c

51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply frequency
(c) increases with the increase in supply frequency
(d) becomes zero with the increase in supply frequency
Ans: c

52. In any A.C. circuit always
(a) apparent power is more than actual power
(b) reactive power is more than apparent power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a

53. Which of the following circuit component opposes the change in the circuit voltage ?
(a) Inductance      
(b) Capacitance
(c) Conductance    
(d) Resistance
Ans:

54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a

55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d

56. Pure inductive circuit takes power from the A.C. line when
(a) applied voltage decreases but cur¬rent increases
(b) applied voltage increases but cur¬rent decreases
(c) both applied voltage and current increase
(d) both applied voltage and current decrease
Ans: a

57. Time constant of a circuit is the time in seconds taken after the application of voltage to each
(a) 25% of maximum value
(b) 50% of maximum value
(c)     63% of maximum value
(d)     90% of the maximum value
Ans: c

58. Time constant of an inductive circuit
(a)     increases with increase of inductance and decrease of resistance
(b)     increases with the increase of inductance and the increase of resis¬tance
(c) increases with the decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a

59. Time constant of a capacitive circuit
(a)     increases with the decrease of capacitance and decrease of resistance
(b)     increases with the decrease of capacitance and increase of resis¬tance
(c) increases with the increase of capacitance and decrease of resis¬tance
(d) increase with increase of capacitance and increase of resis¬tance
Ans: d

60. Magnitude of current at resonance in R-L-C circuit
(a) depends upon the magnitude of R
(b) depends upon the magnitude of L
(c) depends upon the magnitude of C
(d) depends upon the magnitude of R, LandC
Ans: a

61. In a R-L-C circuit
(a) power is consumed in resistance and is equal to I R
(b) exchange of power takes place between inductor and supply line
(c) exchange of power takes place between capacitor and supply line
(d) exchange of power does not take place between resistance and the supply line
(e)     all above are correct
Ans: e

62. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of
(a) R only
(b) L only
(c)C only
(d)LorC
(e) R,LorC
Ans: d

63. In a series L-C circuit at the resonant frequency the
(a) current is maximum
(b) current is minimum
(c) impedance is maximum
(d) voltage across C is minimum
Ans: a

64. The time constant of a series R-C circuit is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c

65. If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be
(a) 0.001 s
(b) 0.1 s
(c) 10 s
(d) 100 s
Ans: b

66. Which of the following coil will have large resonant frequency ?
(a) A coil with large resistance
(b) A coil with low resistance
(c) A coil with large distributed capacitance
(d) A coil with low distributed capacitance
Ans: c

67. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?
(a) 42.42 sin 3141
(b) 60 sin 25 t
(c) 30 sin 50 t
(d) 84.84 sin 25 t
Ans: a

68. The safest value of current the human body can carry for more than 3 second is
(a) 4 mA
(b) 9 mA
(c) 15 mA
(d) 25 mA
Ans: b

69. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W.
This consumption can be attributed to
(a) the big size of the inductor
(b) the reactance of the inductor
(c) the current flowing in the inductor
(d) the statement given is false
Ans: d

70. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
(a) 12 kW
(b) 22 kW
(c) 32 kW
(d) 64 kW
Ans: c

71. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of
(a)     iron loss in core
(b)     skin effect
(c) increase in temperature
(d) capacitive effect between adjacent coil turns
Ans: a

72. In an AC. circuit, a low value of kVAR compared with kW indicates
(a) low efficiency
(b) high power factor
(c) unity power factor
(d) maximum load current
Ans: b

73. In AC. circuits, laminated iron is invariably used in order to
(a) reduce eddy current loss
(b) increase heat radiation
(c) make assembly cheap and easier
(d) reduce circuit permeability
Ans: a

74. The ratio of active power to apparent power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c

75. All definitions of power factor of a series R-L-C circuit are correct except
(a)     ratio of net reactance and impedance
(b)     ratio of kW and kVA
(c) ratio of J and Z
(d) ratio of W and VA
Ans: a

76. The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is
(a) 4 kVAR
(b) 6 kVAR
(c) 8 kVAR
(d) 16 kVAR
Ans: b

77. What will be the phase angle between two alternating waves of equal frequency, when one wave attains maxi¬
mum value the other is at zero value ?
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Ans: c

78. The purpose of a parallel circuit resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b

79. In an A.C. circuit power is dissipated in
(a)     resistance only
(b)     inductance only
(c) capacitance only
(d) none of the above
Ans: a

80. In a parallel R-C circuit, the current always______the applied voltage
(a)     lags
(b)     leads
(c) remains in phase with
(d) none of the above
Ans: b

81. At very low frequencies a series R-C circuit behaves as almost purely
(a)     resistive
(b)     inductive
(c) capacitive
(d) none of the above
Ans: c

82. Skin effect occurs when a conductor carries current at frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d

83. At ______ frequencies the parallel R-L circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d

84. In a sine wave the slope is constant
(a)     between 0° and 90°
(b)     between 90° and 180°
(c) between 180° and 270°
(d) no where
Ans: d

85. The  power is measured in terms of decibles in case of
(a)     electronic equipment
(b)     transformers
(c) current transformers
(d) auto transformers
Ans: a

86. Capacitive susceptance is a measure of
(a)     reactive power in a circuit
(b)     the extent of neutralisation of reactive power in a circuit
(c) a purely capacitive circuit's ability to pass current
(d) a purely capacitive circuit's ability to resist the flow of current
Ans: c

87. Which of the following statements pertains to resistors only ?
(a)     can dissipate considerable amount of power
(6)     can act as energy storage devices
(c) connecting them in parallel in¬creases the total value
(d) oppose sudden changes in voltage
Ans: a

88. Which of the following refers to a parallel circuit ?
(a)     The current through each element is same
(b)     The voltage across element is in proportion to it's resistance value
(c) The equivalent resistance is greater than any one of the resistors
(d) The current through any one element is less than the source current
Ans: d

89. Aphasoris
(a) a line which represents the mag¬nitude and phase of an alternating quantity
(b) a line representing the magnitude and direction of an alternating quantity
(c)     a coloured tag or band for distinction between different phases of a 3-phase supply
(d)     an instrument used for measuring phases of an unbalanced 3-phase load
Ans: a

89. A parallel AC. circuit in resonance will
(a) have a high voltage developed across each inductive and capacitive section
(b) have a high impedance
(c) act like a resistor of low value
(d) have current in each section equal to the line current
Ans: b

90. Wire-wound resistors are unsuitable for use at high frequencies because they
(a) create more electrical noise
(b) are likely to melt under excessive eddy current heat
(c) consume more power
(d) exhibit unwanted inductive and capacitive effects
Ans: d

91. The inductance of a coil can be increased by
(a)     increasing core length
(b)     decreasing the number of turns
(c) decreasing the diameter of the former
(d) choosing core material having high relative permeability
Ans: d

92. In a three-phase supply floating neutral is undesirable because it way give rise to
(a) high voltage across the load
(b) low voltage across the load
(c) unequal line voltages across the load
Ans: c

93. Which of the following waves has the highest value of peak factor ?
(a) Square wave  
(b) Sine wave
(c) Half wave rectified sine wave
(d) Triangular wave
Ans: c

94. The frequency of domestic power supply in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d

95. The r.m.s. value of half wave rectified sine wave is 200 V. The r.m.s. value of full wave rectified AC. will be
(a) 282.8 V
(b) 141.4 V
(c) 111 V
(d) 100 V
Ans: a

96. The r.m.s. value of pure cosine function is
(a) 0.5 of peak value
(b) 0.707 of peak value
(c) same as peak value
(d) zero
Ans: b

97. Ohm is unit of all of the following except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d)     capacitance
Ans: d

98. The series ;nd parallel resonance on L-C circui' differs in that
(a) series resistance needs a low-resistance ource for sharp rise in current
(b) series resonance needs a high-resistance source for sharp increase in current
(c) parallel resonance needs a low-resistance source for a sharp in¬crease in impedance
(d) parallel resonance needs a low-resistance source for a sharp rise in line current
Ans: a

99. The phasors for which of the following pair are 180° out of phase for VL, VC and VR?
(a) Vc and VR
(b) VL and VR
(c) Vc and VL
(d) none of the above
Ans: c

100.   The frequency of an alternating current is
(a) the speed with which the alternator runs
(b) the number of cycles generated in one minute
(c) the number of waves passing through a point in one second
(d) the number of electrons passing through a point in one second
Ans: c

101. A pure capacitor connected across an A.C. voltage consumed 50 W. This is due to
(a) the capacitive reactance in ohms
(b) the current flowing in capacitor
(c) the size of the capacitor being quite big
(d) the statement is incorrect
Ans: d

102. The power factor of a D.C. circuit is always
(a) less than unity
(b) unity
(c) greater than unity
(d) zero
Ans: b

103. The product of apparent power and cosine of the phase angle between circuit voltage and current is
(a) true power
(b) reactive power
(c) volt-amperes
(d) instantaneous power
Ans: a

104. The equation of 50 Hz current sine wave having r.m.s. value of 60 A is
(a) 60 sin 25 t
(b) 60 sin 50 t
(c) 84.84 sin 3141
(d) 42.42 sin 314 t
Ans: c

105. An A.C. voltage is impressed across a pure resistance of 3.5 ohms in parallel with a pure inductance of impedance of 3.5 ohms,
(a) the current through the resistance is more
(b) the current through the resistance is less
(c) both resistance and inductance carry equal currents
(d) none of the above
Ans: c

106. In a pure inductive circuit if the supply frequency is reduced to 1/2, the current will
(a)     be reduced by half
(b)     be doubled
(c) be four times as high
(d) be reduced to one fourth
Ans: b

107. In a pure capacitive circuit if the supply frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times at high
(d) be reduced to one fourth
Ans: a

108. When an alternating current passes through an ohmic resistance the electrical power converted into heat is
(a) apparent power
(b) true power
(c) reactive power
(d) none of the above
Ans: b

109. In each of the three coils of a three phase generator, an alternating voltage having an r.m.s. value of 220 V is induced. Which of the following values is indicated by the voltmeters ?
(a)     220 V
(b)     220V3V
(c) 220/V3 V
(d) none of the above
Ans: a

Latest Circuit Theory Objective type Questions for freshers

Circuit Theory and A.C. Fundamentals Interview Questions and Answers pdf free download

Real Time Circuit Theory and A.C. Fundamentals Interview Questions with Answers PDF

=> Also Read Circuit Theory MCQs

1. What is the definition of a generator? 
   A generator is a machine which converts mechanical energy to electrical energy.
2. What is the definition of an alternator? 
   An AC generator is also called an alternator.
3. With a six pole alternator spinning at 1200 rpm, what would the frequency of the voltage be?        

f=n∗p120=1200∗6120=60Hz$$f=\frac{n\ast p}{120}=\frac{1200\ast 6}{120}=60Hz$$

Circuit Theory Interview Questions and Answers

4. To generate an output frequency of 6oHz, what would be the rpm speed need to be with an eight pole alternator?       

n=120∗fp=120∗608=900RPM$$n=\frac{120\ast f}{p}=\frac{120\ast 60}{8}=900RPM$$

5. In North America what is the standard frequency of AC voltage generated? 
   The standard frequency in North America is 60 Hz
6. With a voltage of 240-V RMS, what would be the peak voltage?

Vp=2–√Vrms=1.414∗240=339V$V_p=\sqrt{2}{V}_{rms}=1.414\ast 240=339V$

7. Using an AC volt meter we found the AC sine wave voltage to be 10-Volts.
   1. Determine the peak value of this voltage. 
      Vp=2–√Vrms=1.414∗10=14.14V$V_p=\sqrt{2}{V}_{rms}=1.414\ast 10=14.14V$
   2. Determine the RMS value of this voltage. 
      Measured voltage is RMS voltage; 10-V rms.
   3. Determine the peak to peak value of this voltage. 
      Peak x 2 = peak to peak; 14.14 x 2 = 28.28 volts peak to peak.
8. List the two single phase voltages in a residential system. 
   120-V and 240-V AC
9. The direction of rotation of an induction motor is affected in what way by interchanging the supply phases? 
   By interchanging the supply phases the motor will run in reverse.
10. When connecting a three phase alternator to the power system, what conditions must be met? 
        1.The phase sequence or rotation of the machine must be the same as that of the system.

              2.The alternator voltage must be in phase with the grid system.

             3.The alternator frequency must be the same as the grid system frequency.

11. The three stator coils of a three phase alternator are positioned apart by how many electrical degrees? 
    The stator coils must be set to 120 degrees apart.
12. There are two basic types of three phase alternator coil connections, what are they?
    The Wye and Delta connections.
13. In an AC resistive circuit, what is the phase relationship between the voltage and current? 
    The current and voltage are in phase.
14. A 10 ohm heater is connected to an AC 340-V peak-to-peak voltage determine:
    1. The peak value of the voltage. 
       340-V/2 = 170-V peak
    2. The effective value of the voltage. 
       1702√=120V$\frac{170}{\sqrt{2}}=120V$
    3. The wattage. 
          120V/10Ω = 12Amps;

                  12A x 120V = 1440 Watts

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