**Latest Circuit Theory Objective Questions For Competitive’s**

**1.For the same peak value which of the following wave will ‘have the highest r.m.s. value ?**

square wave

half wave rectified sine wave

triangular wave

sine wave

**ANSWER : : square wave**

**2.The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.**

90

60

45

30

**ANSWER : : 45**

**3.If two sine waves of the same frequency have a phase difference of JT radians, then**

both will reach their minimum values at the same instant

both will reach their maximum values at the same instant

when one wave reaches its maximum value, the other will reach its minimum value

none of the above

**ANSWER : : when one wave reaches its maximum value, the other will reach its minimum value**

**4.If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is**

a sinusoid of the same frequency

a sinusoid of half the original frequency

a sinusoid of double the frequency

not a sinusoid

**ANSWER : : a sinusoid of the same frequency**

**5.For a sine wave with peak value Emax______8.30. the average value is**

0.636 Emax

0.707 Emax

0.434 EWc

lAUEmax

**ANSWER : : 0.636 Emax**

**6.The r.m.s. value and mean value is the same in the case of**

triangular wave

sine wave

square wave

half wave rectified sine wave

**ANSWER : : square wave**

**7.Two waves of the same frequency have opposite phase when the phase angle between them is**

360�

180�

90�

0�

**ANSWER : : 180�**

**8.The voltage of domestic supply is 220V. This figure represents**

mean value

r.m.s. value

peak value

average value

**ANSWER : : mean value**

**9.Form Factor is the ratio of**

average value/r.m.s. value

average value/peak value

r.m.s. value/average value

r.m.s. value/peak value

**ANSWER : : r.m.s. value/average value**

**10.The phase difference between voltage and current wave through a circuit element is given as 30�. The essential condition is that**

both waves must have same frequency

both waves must have identical peak values

both waves must have zero value at the same time

none of the above

**ANSWER : : both waves must have same frequency**

**11.In a series resonant circuit, the impedance of the circuit is**

minimum

maximum

zero

none of the above

**ANSWER : : minimum**

**12.The peak value of a sine wave is 200 V. Its average value is**

127.4 V

141.4 V

282.8 V

200V

**ANSWER : : 127.4 V**

**13.The period of a wave is**

the same as frequency

time required to complete one cycle

expressed in amperes

none of the above

**ANSWER : : time required to complete one cycle**

**14.For the same peak value, which of the following wave has the least mean value ?**

half wave rectified sine wave

triangular wave

sine wave

square wave

**ANSWER : : half wave rectified sine wave**

**15.The period of a sine wave is _____ seconds. Its frequency is**

20 Hz

30 Hz

40 Hz

50 Hz

**ANSWER : : 50 Hz**

**16.The best place to install a capacitor is**

very near to inductive load

across the terminals of the inductive load

far away from the inductive load

any where

**ANSWER : : across the terminals of the inductive load**

**17.Capacitive reactance is more when**

capacitance is less and frequency of supply is less

capacitance is less and frequency of supply is more

capacitance is more and frequency of supply is less

capacitance is more and frequency of supply is more

**ANSWER : : capacitance is less and frequency of supply is less**

**18.The power consumed in a circuit element will be least when the phase difference between the current and voltage is**

180″

90�

60�

0�

**ANSWER : : 90�**

**19.Form factor for a sine wave is**

1.414

0.707

1.11

0.637

**ANSWER : : 1.11**

**20.A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to**

average voltage

r.m.s. voltage

peak voltage

none of the above

**ANSWER : : r.m.s. voltage**

**21.For a sine wave with peak value Imax the r.m.s. value is**

0.5 Imax

0.707

0.9

1.414 Lmax

**ANSWER : : 0.707**

**22.For a frequency of 200 Hz, the time period will be**

0.05 s

0.005 s

0.0005 s

0.5 s

**ANSWER : : 0.005 s**

**23.The form factor is the ratio of**

peak value to r.m.s. value

r.m.s. value to average value

average value to r.m.s. value

none of the above

**ANSWER : : r.m.s. value to average value**

**24.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.**

2.5

5

10

15

**ANSWER : : 10**

**25.In the case of an unsymmetrical alternating current the average value must always be taken over**

unsymmetrical part of the wave form

the quarter cycle

the half cycle

the whole cycle

**ANSWER : : the whole cycle**

**26.In a loss-free R-L-C circuit the transient current is**

oscillating

square wave

sinusoidal

non-oscillating

**ANSWER : : sinusoidal**

**27.Inductance affects the direct current flow**

only at the time of turning off

only at the time of turning on

at the time of turning on and off

at all the time of operation

**ANSWER : : at the time of turning on and off**

**28.Power factor of the following circuit will be zero**

resistance

inductance

capacitance

both (b) and (c)

**ANSWER : : both (b) and (c)**

**29.In a pure resistive circuit**

current lags behind the voltage by 90�

current leads the voltage by 90�

current can lead or lag the voltage by 90�

current is in phase with the voltage

**ANSWER : : current is in phase with the voltage**

**30.In any A.C. circuit always**

apparent power is more than actual power

reactive power is more than apparent power

actual power is more than reactive power

reactive power is more than actual power

**ANSWER : : apparent power is more than actual power**

**31.The power factor at resonance in R-L- C parallel circuit is**

zero

0.08 lagging

0.8 leading

unity

**ANSWER : : unity**

**32.Power factor of the system is kept high**

to reduce line losses

to maximise the utilization of the capacities of generators, lines and transformers

to reduce voltage regulation of the line

due to all above reasons

**ANSWER : : due to all above reasons**

**33.In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value**

will change the maximum value of current at resonance

will change the resonance frequency

will change the impedance at resonance frequency

will increase the selectivity of the circuit

**ANSWER : : will increase the selectivity of the circuit**

**34.Time constant of an inductive circuit**

increases with increase of inductance and decrease of resistance

increases with the increase of inductance and the increase of resistance

increases with decrease of inductance and decrease of resistance

increases with decrease of inductance and increase of resistance

**ANSWER : : increases with increase of inductance and decrease of resistance**

**35.The square waveform of current has following relation between r.m.s. value and average value.**

r.m.s. value is equal to average value

r.m.s. value of current is greater than average value

r.m.s. value of current is less than average value

none of the above

**ANSWER : : r.m.s. value is equal to average value**

**36.The transient currents are associated with the**

changes in the stored energy in the inductors and capacitors

impedance of the circuit

applied voltage to the circuit

resistance of the circuit

**ANSWER : : changes in the stored energy in the inductors and capacitors**

**37.The time constant of the capacitance circuit is defined as the time during which voltage**

falls to 36.8% of its final steady value

rises to 38.6% of its final steady value

rises to 63.2% of its final steady value

none of the above

**ANSWER : : rises to 63.2% of its final steady value**

**38.In a purely inductive circuit**

actual power is zero

reactive power is zero

apparent power is zero

none of above is zero

**ANSWER : : actual power is zero**

**39.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**

the more heat than produced by A.C. when flowing through the same circuit

the same heat as produced by A.C. when flowing through the same circuit

the less heat than produced by A.C. flowing through the same circuit

none of the above

**ANSWER : : the same heat as produced by A.C. when flowing through the same circuit**

**40.Power factor of the following circuit will be unity**

inductance

capacitance

resistance

both (a) and (b)

**ANSWER : : resistance**

**41.The double energy transient occur in the**

purely inductive circuit

R-L circuit

R-C circuit

R-L-C circuit

**ANSWER : : R-L-C circuit**

**42.In a highly capacitive circuit the**

apparent power is equal to the actual power

reactive power is more than the apparent power

reactive power is more than the actual powetf

actual power is more than its reactive power

**ANSWER : : reactive power is more than the actual powetf**

**43.Power factor of an inductive circuit is usually improved by connecting capacitor to it in**

parallel

series

either (a) or (b)

none of the above

**ANSWER : : parallel**

**44.In a pure inductive circuit**

the current is in phase with the voltage

the current lags behind the voltage by 90�

the current leads the voltage by 90�

the current can lead or lag by 90�

**ANSWER : : the current lags behind the voltage by 90�**

**45.Pure inductive circuit**

consumes some power on average

does not take power at all from a line

takes power from the line during some part of the cycle and then returns back to it during other part of the cycle

none of the above

**ANSWER : : takes power from the line during some part of the cycle and then returns back to it during other part of the cycle**

**46.Inductance of coil**

is unaffected by the supply frequency

decreases with the increase in supply frequency

increases with the increase in supply frequency

becomes zero with the increase in supply frequency

**ANSWER : : increases with the increase in supply frequency**

**47.In a circuit containing R, L and C, power loss can take place in**

C only

L only

R only

all above

**ANSWER : : R only**

**48.All the rules and laws of D.C. circuit also apply to A.C. circuit containing**

capacitance only

inductance only

resistance only

all above

**ANSWER : : resistance only**

**49.In a parallel R-C circuit, the current always______the applied voltage**

lags

leads

remains in phase with

none of the above

**ANSWER : : leads**

**50.The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of**

iron loss in core

skin effect

increase in temperature

capacitive effect between adjacent coil turns

**ANSWER : : iron loss in core**

**51.In an A.C. circuit power is dissipated in**

resistance only

inductance only

capacitance only

none of the above

**ANSWER : : resistance only**

**52.Time constant of a capacitive circuit**

increases with the decrease of capacitance and decrease of resistance

increases with the decrease of capacitance and increase of resis�tance

increases with the increase of capacitance and decrease of resis�tance

increase with increase of capacitance and increase of resis�tance

**ANSWER : : increase with increase of capacitance and increase of resis�tance**

**53.The purpose of a parallel circuit resonance is to magnify**

current

voltage

power

frequency

**ANSWER : : voltage**

**54.Which of the following coil will have large resonant frequency ?**

A coil with large resistance

A coil with low resistance

A coil with large distributed capacitance

A coil with low distributed capacitance

**ANSWER : : A coil with large distributed capacitance**

**55.In AC. circuits, laminated iron is invariably used in order to**

reduce eddy current loss

increase heat radiation

make assembly cheap and easier

reduce circuit permeability

**ANSWER : : reduce eddy current loss**

**56.Time constant of an inductive circuit**

increases with increase of inductance and decrease of resistance

increases with the increase of inductance and the increase of resistance

increases with the decrease of inductance and decrease of resistance

increases with decrease of inductance and increase of resistance

**ANSWER : : increases with increase of inductance and decrease of resistance**

**57.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**

4 kVAR

6 kVAR

8 kVAR

16 kVAR

**ANSWER : : 6 kVAR**

**58.In an AC. circuit, a low value of kVAR compared with kW indicates**

low efficiency

high power factor

unity power factor

maximum load current

**ANSWER : : high power factor**

**59.The time constant of a series R-C circuit is given by**

R/C

RC2

RC

R2C

**ANSWER : : RC**

**60.The ratio of active power to apparent power is known as factor.**

demand

load

power

form

**ANSWER : : power**

**61.The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is**

12 kW

22 kW

32 kW

64 kW

**ANSWER : : 32 kW**

**62.The safest value of current the human body can carry for more than 3 second is**

4 mA

9 mA

15 mA

25 mA

**ANSWER : : 9 mA**

**63.Time constant of a circuit is the time in seconds taken after the application of voltage to each**

25% of maximum value

50% of maximum value

63% of maximum value

90% of the maximum value

**ANSWER : : 63% of maximum value**

**64.If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be**

0.001 s

0.1 s

10 s

100 s

**ANSWER : : 0.1 s**

**65.Pure inductive circuit takes power from the A.C. line when**

applied voltage decreases but cur�rent increases

applied voltage increases but cur�rent decreases

both applied voltage and current increase

both applied voltage and current decrease

**ANSWER : : applied voltage decreases but cur�rent increases**

**66.If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?**

42.42 sin 3141

60 sin 25 t

30 sin 50 t

84.84 sin 25 t

**ANSWER : : 42.42 sin 3141**

**67.What will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value ?**

0�

45�

90�

180�

**ANSWER : : 90�**

**68.A pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to**

the big size of the inductor

the reactance of the inductor

the current flowing in the inductor

the statement given is false

**ANSWER : : the statement given is false**

**69.All definitions of power factor of a series R-L-C circuit are correct except**

ratio of net reactance and impedance

ratio of kW and kVA

ratio of J and Z

ratio of W and VA

**ANSWER : : ratio of net reactance and impedance**

**70.At very low frequencies a series R-C circuit behaves as almost purely**

resistive

inductive

capacitive

none of the above

**ANSWER : : capacitive**

**71.In a series L-C circuit at the resonant frequency the**

current is maximum

current is minimum

impedance is maximum

voltage across C is minimum

**ANSWER : : current is maximum**

**72.Magnitude of current at resonance in R-L-C circuit**

depends upon the magnitude of R

depends upon the magnitude of L

depends upon the magnitude of C

depends upon the magnitude of R, LandC

**ANSWER : : depends upon the magnitude of R**

**73.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,**

the current through the resistance is more

the current through the resistance is less

both resistance and inductance carry equal currents

none of the above

**ANSWER : : both resistance and inductance carry equal currents**

**74.A parallel AC. circuit in resonance will**

have a high voltage developed across each inductive and capacitive section

have a high impedance

act like a resistor of low value

have current in each section equal to the line current

**ANSWER : : have a high impedance**

**75.A pure capacitor connected across an A.C. voltage consumed 50 W. This is due to**

the capacitive reactance in ohms

the current flowing in capacitor

the size of the capacitor being quite big

the statement is incorrect

**ANSWER : : the statement is incorrect**

**76.The frequency of an alternating current is**

the speed with which the alternator runs

the number of cycles generated in one minute

the number of waves passing through a point in one second

the number of electrons passing through a point in one second

**ANSWER : : the number of waves passing through a point in one second**

**77.Wire-wound resistors are unsuitable for use at high frequencies because they**

create more electrical noise

are likely to melt under excessive eddy current heat

consume more power

exhibit unwanted inductive and capacitive effects

**ANSWER : : exhibit unwanted inductive and capacitive effects**

**78.The series ;nd parallel resonance on L-C circui’ differs in that**

series resistance needs a low-resistance ource for sharp rise in current

series resonance needs a high-resistance source for sharp increase in current

parallel resonance needs a low-resistance source for a sharp in�crease in impedance

parallel resonance needs a low-resistance source for a sharp rise in line current

**ANSWER : : series resistance needs a low-resistance ource for sharp rise in current**

**79.Which of the following refers to a parallel circuit ?**

The current through each element is same

The voltage across element is in proportion to it’s resistance value

The equivalent resistance is greater than any one of the resistors

The current through any one element is less than the source current

**ANSWER : : The current through any one element is less than the source current**

**80.The power is measured in terms of decibles in case of**

electronic equipment

transformers

current transformers

auto transformers

**ANSWER : : electronic equipment**

**81.The power factor of a D.C. circuit is always**

less than unity

unity

greater than unity

zero

**ANSWER : : unity**

**82.The phasors for which of the following pair are 180� out of phase for VL, VC and VR?**

Vc and VR

VL and VR

Vc and VL

none of the above

**ANSWER : : Vc and VL**

**83.The product of apparent power and cosine of the phase angle between circuit voltage and current is**

true power

reactive power

volt-amperes

instantaneous power

**ANSWER : : true power**

**84.Ohm is unit of all of the following except**

inductive reactance

capacitive reactance

resistance

capacitance

**ANSWER : : capacitance**

**85.The inductance of a coil can be increased by**

increasing core length

decreasing the number of turns

decreasing the diameter of the former

choosing core material having high relative permeability

**ANSWER : : choosing core material having high relative permeability**

**85.At ______ frequencies the parallel R-L circuit behaves as purely resistive.**

low

very low

high

very high

**ANSWER : : very high**

**86.The frequency of domestic power supply in India is**

200 Hz

100 Hz

60 Hz

50 Hz

**ANSWER : : 50 Hz**

**87.Which of the following statements pertains to resistors only ?**

can dissipate considerable amount of power

can act as energy storage devices

connecting them in parallel in�creases the total value

oppose sudden changes in voltage

**ANSWER : : can dissipate considerable amount of power**

**88.Aphasoris**

a line which represents the mag�nitude and phase of an alternating quantity

a line representing the magnitude and direction of an alternating quantity

a coloured tag or band for distinction between different phases of a 3-phase supply

an instrument used for measuring phases of an unbalanced 3-phase load

**ANSWER : : a line which represents the mag�nitude and phase of an alternating quantity**

**89.Capacitive susceptance is a measure of**

reactive power in a circuit

the extent of neutralisation of reactive power in a circuit

a purely capacitive circuit’s ability to pass current

a purely capacitive circuit’s ability to resist the flow of current

**ANSWER : : a purely capacitive circuit’s ability to pass current**

**90.The r.m.s. value of pure cosine function is**

0.5 of peak value

0.707 of peak value

same as peak value

zero

**ANSWER : : 0.707 of peak value**

**91.The equation of 50 Hz current sine wave having r.m.s. value of 60 A is**

60 sin 25 t

60 sin 50 t

84.84 sin 3141

42.42 sin 314 t

**ANSWER : : 84.84 sin 3141**

**92.In a three-phase supply floating neutral is undesirable because it way give rise to**

high voltage across the load

low voltage across the load

unequal line voltages across the load

unequal line voltages across the load

**ANSWER : hich of the following waves has the highest value of peak factor ?**

**93.In a sine wave the slope is constant**

between 0� and 90�

between 90� and 180�

between 180� and 270�

no where

**ANSWER : : no where**

**94.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**

282.8 V

141.4 V

111 V

100 V

**ANSWER : : 282.8 V**

**95.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 ?**

220 V

220V3V

220/V3 V

none of the above

**ANSWER : : 220 V**

**96.In a pure capacitive circuit if the supply frequency is reduced to 1/2, the current will**

be reduced by half

be doubled

be four times at high

be reduced to one fourth

**ANSWER : : be reduced by half**

**97.When an alternating current passes through an ohmic resistance the electrical power converted into heat is**

apparent power

true power

reactive power

none of the above

**ANSWER : : true power**