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1.

A sinusoidal voltage v = 50sinωt is applied to a series RL circuit. The current in the circuit is given by I = 25sin (ωt-53⁰). Determine the average power.(a) 365(b) 370(c) 375(d) 380This question was addressed to me during an interview for a job.The query is from Reactive Power in section Power and Power Factor of Network Theory

Answer» CORRECT answer is (c) 375

Explanation: The average POWER, Pavg = VeffIeffcosθ. We know the values of Veff, Ieff are Veff = 625 and Ieff – 0.6. So THEAVERAGE power = 625 X 0.6 = 375W.
Discussion
2.

A sinusoidal voltage v = 50sinωt is applied to a series RL circuit. The current in the circuit is given by I = 25sin (ωt-53⁰). Find the power factor.(a) 0.4(b) 0.5(c) 0.6(d) 0.7This question was addressed to me during an internship interview.This intriguing question originated from Reactive Power in chapter Power and Power Factor of Network Theory

Answer»

The correct option is (c) 0.6

Easiest explanation: In sinusoidal sources the power FACTOR is the COSINE of the phase angle between the VOLTAGE and the CURRENT. The expression of power factor = cosθ = cos53⁰ = 0.6.
Discussion
3.

A sinusoidal voltage v = 50sinωt is applied to a series RL circuit. The current in the circuit is given by I = 25sin (ωt-53⁰). Determine the apparent power (VA).(a) 620(b) 625(c) 630(d) 635I had been asked this question in unit test.Origin of the question is Reactive Power in portion Power and Power Factor of Network Theory

Answer»

Correct choice is (C) 630

To explain I would say: The EXPRESSION of apparent POWER (VA) is Papp= VeffIeff = (Vm/√2)×(Im/√2). On substituting the values Vm = 50, Im = 25, we get apparent power = (50×25)/2 = 625VA.
Discussion
4.

The average power (Pavg) is expressed as?(a) Pasecθ(b) Patanθ(c) Pacosθ(d) PasinθThis question was addressed to me at a job interview.The query is from Reactive Power in portion Power and Power Factor of Network Theory

Answer»

The correct option is (c) Pacosθ

For explanation I would say: The AVERAGE POWER is the product of the apparent power and cosθ. The average power (PAVG) is EXPRESSED as Pacosθ. Average power = Pacosθ.
Discussion
5.

The equation of reactive power is?(a) Pacosθ(b) Pasecθ(c) Pasinθ(d) PatanθThe question was asked during an internship interview.Question is from Reactive Power topic in section Power and Power Factor of Network Theory

Answer»

Correct option is (c) Pasinθ

The best explanation: The reactive POWER is the product of the apparent power and sinθ. The EQUATION of reactive power is Pasinθ. Reactive power = Pasinθ.
Discussion
6.

The expression of reactive power (Pr) is?(a) VeffImsinθ(b) VmImsinθ(c) VeffIeffsinθ(d) VmIeffsinθThis question was posed to me in semester exam.My question is taken from Reactive Power in section Power and Power Factor of Network Theory

Answer»

Correct choice is (C) VeffIeffsinθ

Best explanation: The EXPRESSION of reactive power (Pr) is VeffIeffsinθ Volt Amperes Reactive (VAR). Reactive power = VeffIeffsinθ Volt Amperes Reactive (VAR).
Discussion
7.

The expression of true power (Ptrue) is?(a) Pasinθ(b) Pacosθ(c) Patanθ(d) PasecθI have been asked this question in homework.This question is from Reactive Power in chapter Power and Power Factor of Network Theory

Answer»

The CORRECT answer is (b) Pacosθ

The best EXPLANATION: True POWER is the product of the apparent power and cosθ. The EXPRESSION of true power (Ptrue) is Pacosθ. True power = Pacosθ.
Discussion
8.

The power factor is the ratio of ________ power to the ______ power.(a) average, apparent(b) apparent, reactive(c) reactive, average(d) apparent, averageI got this question in examination.The above asked question is from Reactive Power topic in division Power and Power Factor of Network Theory

Answer»

The CORRECT ANSWER is (a) average, APPARENT

Best explanation: The power FACTOR is the ratio of average power to the apparent power. Power factor = (average power)/(apparent power).
Discussion
9.

Reactive power is expressed in?(a) Watts (W)(b) Volt Amperes Reactive (VAR)(c) Volt Ampere (VA)(d) No unitsThe question was posed to me in semester exam.Asked question is from Reactive Power in chapter Power and Power Factor of Network Theory

Answer»

Correct option is (b) VOLT Amperes Reactive (VAR)

The best I can explain: Reactive POWER is expressed in Volt Amperes Reactive (VAR) and power is expressed in watts and apparent power is expressed in Volt Ampere (VA).
Discussion
10.

The reactive power equation (Pr) is?(a) Ieff^2 (ωL)sin2(ωt+θ)(b) Ieff^2 (ωL)cos2(ωt+θ)(c) Ieff^2 (ωL)sin(ωt+θ)(d) Ieff^2 (ωL)cos(ωt+θ)I got this question by my school principal while I was bunking the class.My question is based upon Reactive Power in portion Power and Power Factor of Network Theory

Answer»

Correct choice is (a) Ieff^2 (ωL)SIN2(ωt+θ)

The best EXPLANATION: If we CONSIDER a circuit consisting of a pure INDUCTOR, the power in the inductor is reactive power and the reactive power EQUATION (Pr) is Pr =Ieff^2 (ωL)sin2(ωt+θ).
Discussion
11.

The term lagging power factor is used in which circuits?(a) RLC(b) RC(c) RL(d) LCThe question was posed to me in final exam.I'm obligated to ask this question of Apparent Power and Power Factor in division Power and Power Factor of Network Theory

Answer»

The correct ANSWER is (C) RL

Easy explanation: The term lagging POWER factor is used in RL circuits and not in RLC circuits and RC circuits and LC circuits.
Discussion
12.

The power factor is called leading power factor in case of ____ circuits.(a) LC(b) RC(c) RL(d) RLCI had been asked this question by my college professor while I was bunking the class.This is a very interesting question from Apparent Power and Power Factor in chapter Power and Power Factor of Network Theory

Answer» RIGHT option is (b) RC

To explain: The power FACTOR is called LEADING power factor in case of RC circuits and not in RLC circuits and RL circuits and LC circuits.
Discussion
13.

The power factor=?(a) sinθ(b) cosθ(c) tanθ(d) secθI have been asked this question in an interview for job.This intriguing question originated from Apparent Power and Power Factor in portion Power and Power Factor of Network Theory

Answer»

Correct CHOICE is (b) cosθ

To elaborate: The EXPRESSION of power FACTOR is power factor= cosθ. As the phase angle between the voltage and the current increases the power factor DECREASES.
Discussion
14.

The power factor is the ratio of ________ power to the ______ power.(a) average, apparent(b) apparent, reactive(c) reactive, average(d) apparent, averageThis question was addressed to me in class test.I'm obligated to ask this question of Apparent Power and Power Factor topic in section Power and Power Factor of Network Theory

Answer» RIGHT choice is (a) average, apparent

To explain I WOULD say: The power factor is the ratio of average power to the apparent power. Power factor =(average power)/(apparent power). Power factor is also defined as the factor with which the volt AMPERES are to be multiplied to get true power in the circuit.
Discussion
15.

The expression of apparent power (Papp) is?(a) VmIm(b) VmIeff(c) VeffIeff(d) VeffImI have been asked this question in class test.Query is from Apparent Power and Power Factor topic in section Power and Power Factor of Network Theory

Answer»

Correct choice is (c) VeffIeff

For EXPLANATION I WOULD say: In case of sinusoidal voltage applied to the circuit, the PRODUCT of voltage and the CURRENT is not the true power or average power and it is apparent power. The expression of apparent power (Papp) is Papp = VeffIeff.
Discussion
16.

Average power is also called?(a) apparent power(b) reactive power(c) true power(d) instantaneous powerThe question was asked in final exam.I want to ask this question from Apparent Power and Power Factor topic in section Power and Power Factor of Network Theory

Answer» CORRECT choice is (C) TRUE power

Easy explanation: The AVERAGE power is expressed in watts. It means the useful power transferred from the SOURCE to the load, which is also called true power. Average power is also called true power.
Discussion
17.

If we apply a sinusoidal voltage to a circuit, the product of voltage and current is?(a) true power(b) apparent power(c) average power(d) reactive powerI got this question in an online interview.My enquiry is from Apparent Power and Power Factor topic in division Power and Power Factor of Network Theory

Answer»

Correct CHOICE is (b) apparent POWER

Best explanation: If we apply a sinusoidal VOLTAGE to a circuit, the product of voltage and CURRENT is apparent power. The apparent power is expressed in volt amperes or simply VA.
Discussion
18.

For reactive load, the power factor is equal to?(a) 0(b) 1(c) 2(d) 3This question was posed to me in an international level competition.The doubt is from Apparent Power and Power Factor topic in section Power and Power Factor of Network Theory

Answer»

The CORRECT option is (a) 0

For explanation: For reactive LOAD, the POWER factor is equal to 0. Power factor = 0 when current to a load is 90⁰ out of phase with the voltage.
Discussion
19.

If power factor = 0, then the current to a load is ______ with the voltage.(a) in phase(b) out of phase(c) 45⁰ out of phase(d) 90⁰ out of phaseI had been asked this question during an interview for a job.This key question is from Apparent Power and Power Factor topic in division Power and Power Factor of Network Theory

Answer»

The CORRECT answer is (d) 90⁰ out of phase

To EXPLAIN I WOULD say: If the power factor = 0, then the current to a load is 90⁰ out of phase with the VOLTAGE and it happens in case of reactive load.
Discussion
20.

If power factor = 1, then the current to the load is ______ with the voltage across it.(a) out of phase(b) in phase(c) 90⁰ out of phase(d) 45⁰ out of phaseThis question was posed to me in exam.I would like to ask this question from Apparent Power and Power Factor in portion Power and Power Factor of Network Theory

Answer»

Correct answer is (b) in PHASE

The explanation is: If POWER factor = 1, then the CURRENT to the LOAD is in phase with the voltage across it because the expression of power factor is power factor = cosθ.
Discussion
21.

In case of resistive load, what is the power factor?(a) 4(b) 3(c) 2(d) 1This question was posed to me in an interview for job.Enquiry is from Apparent Power and Power Factor in portion Power and Power Factor of Network Theory

Answer» CORRECT answer is (d) 1

The BEST I can explain: In CASE of resistive load, the power factor = 1 as the current to the load is in PHASE with the voltage across it.
Discussion
22.

The highest power factor will be?(a) 1(b) 2(c) 3(d) 4I had been asked this question at a job interview.Origin of the question is Apparent Power and Power Factor topic in portion Power and Power Factor of Network Theory

Answer»

Correct choice is (a) 1

Explanation: The power factor is USEFUL in determining the useful power transferred to a load. The HIGHEST power factor will be 1.
Discussion
23.

Determine the average power delivered to the circuit consisting of an impedance Z = 5+j8 when the current flowing through the circuit is I = 5∠30⁰.(a) 61.5(b) 62.5(c) 63.5(d) 64.5This question was addressed to me in semester exam.Query is from Average Power topic in section Power and Power Factor of Network Theory

Answer» CORRECT answer is (b) 62.5

Explanation: The expression of the average power delivered to the CIRCUIT is Pavg = IM^2 R/2. Given Im = 5, R = 5. So the average power delivered to the circuit = 5^2×5/2 = 62.5W.
Discussion
24.

A voltage v (t) = 100sinωt is applied to a circuit. The current flowing through the circuit is i(t) = 15sin(ωt-30⁰). Determine the average power delivered to the circuit.(a) 620(b) 630(c) 640(d) 650This question was posed to me during an online exam.This interesting question is from Average Power topic in portion Power and Power Factor of Network Theory

Answer»

Correct option is (d) 650

The BEST EXPLANATION: The expression of average power delivered to the circuit is Pavg = VeffIeffcosθ, θ = 30⁰. We have Veff = 71, Ieff = 11. So the average power delivered to the circuit Pavg = 71 x 11 x COS 30⁰ = 650W.
Discussion
25.

A voltage v (t) = 100sinωt is applied to a circuit. The current flowing through the circuit is i(t) = 15sin(ωt-30⁰). Find the effective value of current.(a) 9(b) 10(c) 11(d) 12This question was addressed to me during an online exam.The query is from Average Power in chapter Power and Power Factor of Network Theory

Answer»

Correct CHOICE is (c) 11

For EXPLANATION: The expression of EFFECTIVE value of current is Ieff = Im/√2. GivenIm = 15. On SUBSTITUTING the value in the equation we get effective value of current = 15/√2 = 11V.
Discussion
26.

A voltage v (t) = 100sinωt is applied to a circuit. The current flowing through the circuit is i(t) = 15sin(ωt-30⁰). Find the effective value of voltage.(a) 70(b) 71(c) 72(d) 73I have been asked this question in an online quiz.This intriguing question originated from Average Power in division Power and Power Factor of Network Theory

Answer»

Right choice is (B) 71

Easiest explanation: The EXPRESSION of EFFECTIVE value of VOLTAGE is Veff = Vm/√2. GivenVm = 100. On substituting the value in the equation we get effective value of voltage = 100/√2 = 71V.
Discussion
27.

If a circuit has complex impedance, the average power is ______(a) power stored in inductor only(b) power stored in capacitor only(c) power dissipated in resistor only(d) power stored in inductor and power dissipated in resistorI had been asked this question during an interview.My enquiry is from Average Power in division Power and Power Factor of Network Theory

Answer»

Correct OPTION is (c) power DISSIPATED in resistor only

Best explanation: If a circuit has COMPLEX impedance, the average power is power dissipated in resistor only and is not stored in capacitor or INDUCTOR.
Discussion
28.

In case of purely inductive circuit, average power = ____ and θ = ______(a) 0, 90⁰(b) 1, 90⁰(c) 1, 0⁰(d) 0, 0⁰I got this question in final exam.This key question is from Average Power topic in portion Power and Power Factor of Network Theory

Answer» RIGHT choice is (a) 0, 90⁰

To ELABORATE: In case of PURELY inductive circuit, the PHASE angle between the voltage and current is zero that is θ=90⁰. Hence the average power = 0.
Discussion
29.

In case of purely capacitive circuit, average power = ____ and θ = _____(a) 0, 0⁰(b) 1, 0⁰(c) 1, 90⁰(d) 0, 90⁰This question was posed to me by my college director while I was bunking the class.My question is based upon Average Power topic in section Power and Power Factor of Network Theory

Answer» CORRECT ANSWER is (d) 0, 90⁰

Easy EXPLANATION: In case of purely capacitive circuit, the phase angle between the voltage and CURRENT is zero that is θ=90⁰. Hence the average power = 0.
Discussion
30.

In case of purely resistive circuit, the average power is?(a) VmIm(b) VmIm/2(c) VmIm/4(d) VmIm/8This question was addressed to me in class test.My doubt is from Average Power in division Power and Power Factor of Network Theory

Answer»

The correct choice is (b) VmIm/2

For explanation I WOULD say: In case of purely resistive circuit, the PHASE ANGLE between the voltage and CURRENT is ZERO that is θ=0⁰. Hence the average power = VmIm/2.
Discussion
31.

Average power (Pavg)=?(a) VeffImcosθ(b) VeffIeffcosθ(c) VmImcosθ(d) VmIeffcosθThe question was asked in final exam.The query is from Average Power in portion Power and Power Factor of Network Theory

Answer»

Right option is (b) VeffIeffcosθ

Easy explanation: To get AVERAGE power we have to take the product of the effective VALUES of both voltage and current multiplied by cosine of the PHASE angle between the voltage and current. The expression of average power is Average power (PAVG) = VeffIeffcosθ
Discussion
32.

The equation of the average power (Pavg) is?(a) (VmIm/2)cosθ(b) (VmIm/2)sinθ(c) VmImcosθ(d) VmImsinθThis question was posed to me by my college professor while I was bunking the class.Question is from Average Power in chapter Power and Power Factor of Network Theory

Answer»

Correct OPTION is (a) (VmIm/2)cosθ

Explanation: To find the AVERAGE value of any power function we have to take a particular TIME interval from T1 to t2, by INTEGRATING the function we get the average power. The equation of the average power (Pavg) is Pavg = (VmIm/2)cosθ.
Discussion
33.

At θ=π/2, positive portion is __________ negative portion in power cycle.(a) greater than(b) less than(c) equal to(d) greater than or equal toI had been asked this question in an interview for job.My doubt is from Instantaneous Power in division Power and Power Factor of Network Theory

Answer»

Correct option is (C) equal to

For EXPLANATION: At θ=π/2, the AREA under positive portion is equal to the area under NEGATIVE portion in power cycle. At this instant the power dissipated in the CIRCUIT is zero.
Discussion
34.

The time varying part in the equation of instantaneous power has frequency ________________ that of the frequency of voltage or current wave forms.(a) equal to(b) twice(c) thrice(d) four timesThe question was asked in an interview.This is a very interesting question from Instantaneous Power topic in division Power and Power Factor of Network Theory

Answer»

Right choice is (b) TWICE

Easy explanation: The time VARYING part in the EQUATION of instantaneous power has a frequency twice that of voltage or CURRENT wave forms and the other part is a fixed part.
Discussion
35.

In P (t) equation, if θ=0, then P (t) =?(a) (VmIm/2)(1+cos⁡ωt)(b) (VmIm/2)(cos⁡ωt)(c) (VmIm/2)(cos⁡2ωt)(d) (VmIm)(1+cos⁡2ωt)This question was posed to me during an interview.Query is from Instantaneous Power topic in portion Power and Power Factor of Network Theory

Answer»

Right option is (d) (VmIm)(1+cos⁡2ωt)

To elaborate: In P (t) equation, if θ=0⁰, then P (t) =(VmIm/2)(1+cos⁡2ωt). The POWER WAVE has a frequency twice that of the voltage or CURRENT. Here the AVERAGE value of power is VmIm/2.
Discussion
36.

The average value of power if θ=0⁰ is?(a) VmIm/2(b) VmIm/2(c) VmIm/4(d) VmIm/8This question was posed to me in an interview.Asked question is from Instantaneous Power topic in chapter Power and Power Factor of Network Theory

Answer»

The CORRECT ANSWER is (B) VmIm/2

The explanation is: The average value of power if θ=0⁰ is VmIm/2. So, average power = VmIm/2 at θ=0⁰. When PHASE angle is increased the negative portion of the power cycle INCREASES and lesser power is dissipated.
Discussion
37.

Instantaneous power is negative, when the polarities of voltage and current are of __________(a) opposite sign(b) same sign(c) voltage is zero(d) current is zeroI have been asked this question by my college professor while I was bunking the class.My question is taken from Instantaneous Power topic in division Power and Power Factor of Network Theory

Answer»

Correct CHOICE is (a) opposite sign

To explain: INSTANTANEOUS power is NEGATIVE, when voltage and CURRENT have opposite sign that is if voltage is POSITIVE, the current is negative and if current is positive, the voltage is negative.
Discussion
38.

The equation of instantaneous power is?(a) P (t) = (VmIm/2)(cos⁡(2ωt+θ)+sin⁡θ)(b) P (t) = (VmIm/2)(sin⁡(2ωt+θ)+cos⁡θ)(c) P (t) = (VmIm/2)(cos⁡(2ωt+θ)+cos⁡θ)(d) P (t) = (VmIm/2)(sin⁡(2ωt+θ)+sin⁡θ)The question was posed to me in an online interview.This interesting question is from Instantaneous Power topic in chapter Power and Power Factor of Network Theory

Answer»

Right option is (c) P (t) = (VmIm/2)(cos⁡(2ωt+θ)+cos⁡θ)

To ELABORATE: The equation of INSTANTANEOUS power is P (t) = (VmIm/2)(cos⁡(2ωt+θ)+cos⁡θ). It consists of two parts. One is a fixed part and the other is TIME VARYING which has frequency twice that of the voltage or current wave FORMS.
Discussion
39.

If there is complex impedance in a circuit, part of energy is ____________ by reactive part and part of its energy is ____________ by the resistance.(a) alternately stored and returned, alternately stored and returned(b) alternately stored and returned, dissipated(c) dissipated, alternately stored and returned(d) dissipated, dissipatedI had been asked this question in my homework.The question is from Instantaneous Power topic in chapter Power and Power Factor of Network Theory

Answer»

Right option is (b) ALTERNATELY stored and returned, dissipated

Easy explanation: If there is complex IMPEDANCE in a circuit, part of energy is alternately stored and returned by reactive part and part of its energy is dissipated by the resistance. The amount of energy dissipated is determined by RELATIVE VALUES of resistance and reactance.
Discussion
40.

In capacitor, the energy delivered by source is ____________ by capacitor.(a) returned to source(b) dissipated in the form of heat(c) stored as electric field(d) stored as magnetic fieldI had been asked this question by my school principal while I was bunking the class.This interesting question is from Instantaneous Power topic in section Power and Power Factor of Network Theory

Answer»

Correct answer is (c) stored as electric field

Best explanation: In capacitor, the ENERGY delivered by source is stored as electric field by capacitor and is not stored as MAGNETIC field or DISSIPATED in the FORM of heat.
Discussion
41.

In inductor, the energy delivered by source is ____________ by inductor.(a) stored as magnetic field(b) dissipated in the form of heat(c) returned to source(d) stored as electric fieldThe question was posed to me in quiz.Enquiry is from Instantaneous Power topic in division Power and Power Factor of Network Theory

Answer»

Right answer is (a) stored as MAGNETIC field

The BEST I can explain: In inductor, the energy DELIVERED by source is stored as magnetic field by inductor and is not dissipated in the FORM of HEAT or stored as electric field.
Discussion
42.

In purely resistive circuit, energy delivered by source is ____________ by resistance.(a) dissipated in the form of heat(b) stored as electric field(c) stored as magnetic field(d) returned to sourceI got this question in a national level competition.The above asked question is from Instantaneous Power topic in portion Power and Power Factor of Network Theory

Answer»

Correct option is (a) dissipated in the FORM of HEAT

The best I can explain: In purely RESISTIVE circuit, ENERGY delivered by source is dissipated in the form of heat by resistance and is not stored as either electric field or magnetic field.
Discussion