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