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ECE : Networks Analysis and Synthesis - Quiz(MCQ)
1 .
Millman’s theorem yields:
A)
Equivalent resistance
B)
Equivalent impedance
C)
Equivalent voltage source
D)
Equivalent voltage or current source

Correct Answer :   Equivalent voltage or current source

2 .
The superposition theorem is applicable to:
A)
Linear responses only
B)
Linear and nonlinear resistors only
C)
Linear, nonlinear and time variant responses
D)
None of the above

Correct Answer :   Linear responses only

3 .
Kirchhoff's law is applicable to:
A)
A.C. circuits
B)
D.C. circuits
C)
Passive networks only
D)
Both (B) and (C)

Correct Answer :   Both (B) and (C)

4 .
In a minimum function
A)
the degree of numerator and denominator are unequal
B)
the degree of numerator and denominator are equal
C)
the degree of numerator is one less than degree of denominator
D)
the degree of numerator is one more than degree of denominator

Correct Answer :   the degree of numerator and denominator are equal

Explanation : If degrees of numerator and denominator were unequal, a pole or zero can be removed. Such a function cannot be a minimum function. Therefore degrees of numerator and denominator must be equal.

5 .
Henry is equivalent to
A)
Weber/Volt
B)
Volts/Ampere
C)
Weber/Ampere
D)
Weber/Ampere²

Correct Answer :   Weber/Ampere

6 .
An RLC series circuit is underdamped. To make it overdamped, the value of R
A)
has to be increased
B)
has to be decreased
C)
has to be reduced to zero
D)
has to be increased to infinity

Correct Answer :   has to be increased

Explanation : For overdamping R is more.

7 .
A series RLC circuit has a resonant frequency of 1000 Hz. The maximum voltage across C is likely to occur at a frequency of about
A)
975 Hz
B)
1000 Hz
C)
1025 Hz
D)
2000 Hz

Correct Answer :   975 Hz

Explanation : Maximum voltage across capacitance occurs at a frequency slightly less than resonant frequency.

8 .
The resistance of a 230 V, 100 W lamp is
A)
23 Ω
B)
529 Ω
C)
2300 Ω
D)
5290 Ω

Correct Answer :   529 Ω

Explanation :

9 .
In the given circuit, viewed from AB, the circuit can be reduced to an equivalent circuit as
A)
1 volt source in series with 10 Ω resistor
B)
5 volts source in series with 10 Ω resistor
C)
7 volts source in series with 2.4 Ω resistor
D)
15 volts source in series with 2.4 Ω resistor

Correct Answer :   7 volts source in series with 2.4 Ω resistor

Explaination :

10 .
An RC series circuit is charged by a voltage E. After a long time the battery is removed and a short circuit is placed across R-C. Then
A)
the polarity of voltage across R depends on time constant RC
B)
the polarity of voltage across R is same during discharge and during charge
C)
the polarity of voltage across R during discharging is opposite to that during charging
D)
None of the above

Correct Answer :   the polarity of voltage across R during discharging is opposite to that during charging

Explanation : Direction of current during discharging is opposite to that during charging.

11 .
Two coils having self inductances of 10 mH and 40 mH are mutually coupled. The maximum possible mutual inductance is
A)
40 mH
B)
20 mH
C)
10 mH
D)
5 mH

Correct Answer :   20 mH

12 .
An RLC series circuit has R = 7.07 Ω, L = .707 H and C = 7.07 μF. At Half power frequencies the circuit impedance is likely to be
A)
7.07 Ω
B)
10 Ω
C)
14.14 Ω
D)
20 Ω

Correct Answer :   10 Ω

Explaination : At half power frequency the circuit impedance is 2 times resistance.

13 .
Two similar coils have self inductance of 1 mH each. Coefficient of coupling is 0.5. The mutual inductance M is
A)
0.5 mH
B)
0.25 mH
C)
0.707 mH
D)
1 mH

Correct Answer :   0.5 mH

14 .
Two capacitors of 1 μF and 2 μF capacitance are connected in parallel across a 30 V dc battery. After the capacitors have been charged, the charges across the two capacitors will be
A)
30 μC each
B)
60 μC each
C)
30 μC and 60 μC respectively
D)
60 μC and 30 μC respectively

Correct Answer :   30 μC and 60 μC respectively

Explaination :

Q1 = 1 x 10-6 x 30 = 30 μC, Q2 = 2 x 10-6 x 30 = 60 μC.

15 .
A thermistor is used for
A)
over voltage protection
B)
automatic light control
C)
temperature alarm circuit
D)
None of the above

Correct Answer :   temperature alarm circuit

Explanation : The resistance of a thermistor decreases with increases in temperature. It is used to monitor hot spot temperature of electric machines.

16 .
When a lead acid battery is being charged, the specific gravity of the electrolyte
A)
increases
B)
decreases
C)
remains the same
D)
either increases or decreases

Correct Answer :   increases

Explanation : Specific gravity of electrolyte is highest when battery is fully charged and is lowest when discharged.

17 .
A magnetic circuit has an iron length of 20 cm and air gap length 0.1 cm. If μr = 200 then
A)
mmf for iron and air gap are equal
B)
mmf for iron is much less than that for air gap
C)
mmf for iron is much more than that for air gap
D)
Either (A) or (B)

Correct Answer :   mmf for iron and air gap are equal

Explanation :

18 .
Two coils X and Y have self inductances of 5 mH and 10 mH and mutual inductance of 3 mH. If the current in coils X change at a steady rate of 100 A/s, the emf induced in coil Y is
A)
0.3 V
B)
0.5 V
C)
1 V
D)
1.5 V

Correct Answer :   0.3 V

Explaination :

19 .
Two capacitors of 2 μF and 4 μF capacitance are connected in series across a 30 V dc battery. After the capacitors have been charged, the voltage across them will be
A)
10 V and 20 V
B)
20 V and 10 V
C)
15 V each
D)
30 V each

Correct Answer :   20 V and 10 V

Explaination : Charge will be the same. Since Q = C V voltage will be inversely proportional to Q. Hence 20 V and 10 V.

20 .
The frame of an electric motor is earthed through three earthing plates resistances 30 Ω, 20 Ω and 10 Ω respectively. During fault the energy dissipated by three plates are W1, W2 and W3. Then
A)
W1 = W2 = W3
B)
W1 > W2 > W3
C)
W1 + W3 < W2
D)
W1 < W2 < W3

Correct Answer :   W1 < W2 < W3

Explaination : Energy dissipated by the plate with lowest resistance is maximum.

21 .
Two voltages are 50 ∠0 V and 75 ∠ - 60° V. The sum of these voltages is
A)
109 ∠ - 25° V
B)
100 ∠ - 50.1° V
C)
109 ∠ - 36.6° V
D)
109 ∠ - 60° V

Correct Answer :   109 ∠ - 36.6° V

Explaination : 50Ð0 = 50 + j 0.75∠-60° = 37.5 - j 64.95

Sum = (50 + 37.5) - j 64.95 = 87.5 - j 64.95 = 109∠-36.6°

22 .
In an RL series circuit the inductance is 1H and current at an instant is 0.6 A. The energy stored in magnetic field is
A)
0.36 J
B)
0.18 J
C)
0.09 J
D)
0.03 J

Correct Answer :   0.18 J

23 .
In a series ac circuit a voltage of 20 V at 25 Hz causes a current of 0.20 A, while the same voltage at 75 Hz causes a current of 0.12 A. The circuit consists of
A)
R and C in series
B)
R and L in series
C)
R and C in parallel
D)
Either (A) or (B)

Correct Answer :   R and C in series

Explaination : As f increases impedance increases and current decreases in RL circuit.

24 .
In a practical voltage source, the terminal voltage
A)
is always equal to source voltage
B)
is always less than source voltage
C)
cannot be less than source voltage
D)
cannot be higher than source voltage

Correct Answer :   cannot be higher than source voltage

Explanation : A practical voltage source has some source resistance.

Because of voltage drop across source resistance, terminal voltage cannot be higher than source voltage.

If current is zero, terminal voltage and source voltage are equal.

25 .
A series R-L circuit has R = 1 Ω and L = 1 H. It is excited by a V battery at t = 0. The steady state condition is reached at
A)
t = 0 s
B)
t = 0.1 s
C)
t = ∞
D)
t = 1 s

Correct Answer :   t = ∞

Explanation :

i = 10 (1 - e-t). It reaches steadily state value at t = ∞

26 .
The current source in figure, can be replaced by
A)
a voltage source of 20 V in series with 4 Ω resistance
B)
a voltage source of 16 V in series with 5 Ω resistance
C)
a voltage source of 16 V in series with 4 ohm resistance
D)
a voltage source of 20 V in series with 5 ohm resistance

Correct Answer :   a voltage source of 16 V in series with 4 ohm resistance

Explaination : The parallel combination of 20 Ω and 5 Ω is 4 Ω. Therefore, strength of current source is 4 x 4 = 16 A and source resistance is 4 ohms.

27 .
In a purely inductive circuit, the current __________ the voltage by __________ .
A)
lags, 0°
B)
lags, 45°
C)
lags, 90°
D)
leads, 90°

Correct Answer :   lags, 90°

Explanation : In inductive circuit current lags the voltage by 90°.

28 .
The frame of electric motor is connected to three plates having earthing resistance of 10 Ω, 20 Ω and 30 Ω respectively. The materials of the three plates are copper, aluminium and iron respectively. The percentage of energy dissipated by 10 Ω earthing plate
A)
is less than 50% of total energy
B)
is more than 50% of total energy
C)
depends on the materials of the three plates
D)
may be more or less than 50% of total energy

Correct Answer :   is more than 50% of total energy

Explaination : The parallel combination of 30 Ω and 20 Ω is 12 Ω. Since 12 Ω and 10 Ω are in parallel, the 10 ohm plate draws more than 50% current and dissipates more than 50% energy.

29 .
Current having waveform in figure flows through 10 Ω resistance. Average power is
A)
250 W
B)
333.3 W
C)
500 W
D)
1000 W

Correct Answer :   333.3 W

Explaination :

30 .
If A = 16 ∠64°, (A)0.5 is
A)
4∠8°
B)
4∠32°
C)
4∠64°
D)
4∠128°

Correct Answer :   4∠32°

Explaination :

31 .
For a transmission line open circuit and short circuit impedances are 20 Ω and 5 Ω. Then characteristic impedance is
A)
10 Ω
B)
25 Ω
C)
50 Ω
D)
100 Ω

Correct Answer :   10 Ω

32 .
The drift velocity of electrons is
A)
half the speed of light
B)
equal to speed of light
C)
almost equal to speed of light
D)
very small as compared to speed of light

Correct Answer :   very small as compared to speed of light

Explanation : Drift velocity of electrons is very small.

33 .
Wave A = 100 sin ωt and wave B = 100 cos ωt. Then
A)
rms values of A is less than that of B
B)
rms values of A is more than that of B
C)
rms values of the two waves are equal
D)
rms values of the two waves may or may not be equal

Correct Answer :   rms values of the two waves are equal

Explanation : Since peak values are equal, their rms values are equal irrespective of phase difference.

34 .
In an R-C series circuit excited by a voltage E, the charge across capacitor at t = 0+ is
A)
0
B)
CE
C)
CE (1 - e^-t/RC)
D)
None of the above

Correct Answer :   0

Explanation : Voltage across a capacitor cannot change instantaneously.

35 .
A capacitor stores 0.15C at 5 V. Its capacitance is
A)
0.03 μF
B)
0.03 F
C)
0.75 F
D)
0.75 μF

Correct Answer :   0.03 F

Explanation : Q = CV or 0.15 = C(5) or C = 0.03 F.

36 .
A 0.5 μF capacitor is connected across a 10 V battery. After a long time, the circuit current and voltage across capacitor will be
A)
0.05 A and 5 V
B)
0.5 A and 0 V
C)
20 A and 5 V
D)
0 A and 10 V

Correct Answer :   0 A and 10 V

Explanation : When the capacitor is fully charged, i = 0 and voltage across capacitor is equal to battery voltage.

37 .
In figure the voltage drop across the 10 Ω resistance is 10 V. The resistance R
A)
is 6 Ω
B)
is 8 Ω
C)
is 10 Ω
D)
Can not say

Correct Answer :   is 6 Ω

Explaination : Current supplied by battery = 10/10 = 1A. Therefore current through 2Ω resistance is 11 A.
Voltage across R = 48 - 10 - 11 x 2 = 16 V.

38 .
A two branch parallel tuned circuit has a coil of resistance 100 Ω and inductance 0.005 H in one branch and 10 nF capacitor in the second branch. At resonance frequency is
A)
100 rad/sec
B)
1000 rad/sec
C)
10000 rad/sec
D)
more than 10000 rad/sec

Correct Answer :   1000 rad/sec

Explaination :

39 .
A circuit is replaced by its Thevenin's equivalent to find current through a certain branch. If VTH = 10 V and RTH = 20 Ω, the current through the branch
A)
will always be 0.5 A
B)
may be 0.5 A or more or less
C)
will always be less than 0.5 A
D)
will always be equal to or less than 0.5 A

Correct Answer :   will always be equal to or less than 0.5 A

Explaination :

40 .
A capacitor used for power factor correction is single phase circuit decreases
A)
line current
B)
power factor
C)
Both line current and p.f.
D)
the line current and increases p.f.

Correct Answer :   the line current and increases p.f.

Explanation : Capacitor is used to improve (increase) p.f. Therefore, line current is decreased for the same active power.

41 .
Which statement is true for an ac circuit?
A)
Active power is always less than apparent power
B)
Active power is always more than reactive power
C)
Active power cannot be more than apparent power
D)
Active power cannot be more than reactive power

Correct Answer :   Active power cannot be more than apparent power

Explanation : Active and apparent power are equal for resistive circuit. Otherwise active power is less than apparent power.

42 .
Three inductors each 30 mH are connected in delta. The value of inductance or each arm of equivalent star is
A)
10 mH
B)
15 mH
C)
30 mH
D)
90 mH

Correct Answer :   10 mH

43 .
If the iron core of a coil is removed so that it becomes an air cored coil, its inductance
A)
will increase
B)
will decrease
C)
will remain the same
D)
may increase or decrease

Correct Answer :   will decrease

Explanation : μr for air is 1 while μr for iron is more than 1.

44 .
Given Is = 20 A, Vs = 20 V, the current I in the 3 Ω resistance is given by
A)
2 A
B)
4 A
C)
8 A
D)
16 A

Correct Answer :   4 A

Explaination :

45 .
A square current wave of magnitude 1 A is applied to an element for 5 seconds. The voltage across the element rises linearly from 0 to final value linearly. The element is
A)
resistance
B)
inductance
C)
capacitance
D)
R and C in series

Correct Answer :   capacitance

Explaination : Charge across capacitance increases linearly. Since capacitance is constant, voltage increases linearly.

46 .
A periodic voltage v(t) = 1 + 4 sin ωt + 2 cos ωt is applied across a 1 ohm resistance. The power dissipated is
A)
1 W
B)
11 W
C)
21 W
D)
24.5 W

Correct Answer :   11 W

Explanation :

47 .
If A = 4∠7°, A2 is
A)
16∠7°
B)
16∠3.5
C)
16∠49°
D)
16∠14°

Correct Answer :   16∠14°

Explaination :

48 .
A coil is wound having a diameter d. Its inductance is 10 mH. If it is rewound on the same core with a wire having diameter 0.5 d and total weight of the wire is the same as before, the inductance will be
A)
5 mH
B)
10 mH
C)
40 mH
D)
160 mH

Correct Answer :   160 mH

Explaination : Since diameter is halved, area of cross-section is one-fourth. The number of turns becomes four times. Inductance = μ N2.

49 .
A resistance and an inductance are connected in parallel and fed from 50 Hz ac mains. Each branch takes a current of 5 A. The current supplied by source is
A)
5 A
B)
7.07 A
C)
10 A
D)
zero

Correct Answer :   7.07 A

Explaination :

50 .
An RC driving point impedance function has zeros at s = - 2 and s = - 5. The admissible poles are
A)
s = -1 and s = -3
B)
s = 0 and s = -1
C)
s = -3 and s = -4
D)
s = 0 and s = -6

Correct Answer :   s = -1 and s = -3

Explanation : In RC functions poles and zeros are interlaced.

51 .
An RLC series circuit is fed form 100 V ac supply. Inductance is 1 H and Q = 7.5. At resonance, the voltage across inductance is
A)
50 V
B)
100 V
C)
750 V
D)
1500 V

Correct Answer :   750 V

Explanation : Voltage across inductance at resonance = QV = 7.5 X 100 V.

52 .
As temperature increases, the temperature coefficient of a metal
A)
increases
B)
decreases
C)
remains unchanged
D)
Any of the above

Correct Answer :   decreases

Explanation : It at is temperature coefficient at t°C and a0 is temperature coefficient at 0°C.

53 .
A wire has a resistance R ohm. If another wire of the same material and same weight has double the diameter (as compared to the first wire), the resistance of the second wire will be
A)
0.5 R
B)
0.25 R
C)
0.125 R
D)
R/16

Correct Answer :   R/16

Explaination : Since diameter is double, area of cross-section is four times and length is one-fourth.

54 .
Volt is equivalent to
A)
joule/volt
B)
joule/watt
C)
joule/ampere
D)
joule/coulomb

Correct Answer :   joule/coulomb

Explanation :

55 .
A two branch parallel tuned circuit has a capacitance C in one of the two branches and resistance R in second branchs. As C is decreased the dynamic resistance
A)
increases
B)
decreases
C)
remains constant
D)
may increases or decreases

Correct Answer :   increases

Explanation : Dynamic resistance = L/RC and increases as C is decreased.

56 .
Find RL for maximum power transfer
A)
1.125 Ω
B)
3 Ω
C)
4.17 Ω
D)
None of the above

Correct Answer :   3 Ω

Explaination :

57 .
In an R-C circuit, the impedance is 40 Ω at a frequency of 100 Hz. At 200 Hz the impedance should be
A)
20 Ω
B)
40 Ω
C)
80 Ω
D)
more than 20 Ω but less than 40 Ω

Correct Answer :   more than 20 Ω but less than 40 Ω

58 .
An RL series circuit has an impedance of 20 Ω when frequency is 25 Hz. At f= 50 Hz, the impedance will be
A)
20 Ω
B)
40 Ω
C)
less than 20 W but more than 10 Ω
D)
less than 40 W but more than 20 Ω

Correct Answer :   40 Ω

59 .
The resistance of the circuit shown is figure is
A)
5 Ω
B)
More than 4 Ω
C)
More than 6 Ω
D)
Between 6 and 7 Ω

Correct Answer :   5 Ω

Explaination : The parallel combination of 3, 5 and 4 ohm is short-circuited. Therefore their net resistance is zero.

60 .
The self inductances of two coils are 27 H and 3 H. If the winding or coils is such that 50% of flux of one links the other, the mutual inductance is
A)
4.5 H
B)
9 H
C)
24 H
D)
30 H

Correct Answer :   4.5 H

Explaination :

61 .
For H(s) to be positive real, the condition Re[H(jω)] ≥ 0 for 0 ≤ ω ≤ ∞ is
A)
a sufficient condition
B)
a necessary condition
C)
is not a necessary condition
D)
a necessary and sufficient condition

Correct Answer :   a necessary condition

Explaination : H(s) must possess two more properties if it is positive real.

62 .
n a specimen of cast iron, a field strength of 400 AT/m cause a flux density of 0.6 T. In a specimen of silicon steel, the same value of H would cause B to be
A)
0.6 T
B)
less than 0.6 T
C)
more than 0.6 T
D)
0.6 T or less than 0.6 T

Correct Answer :   0.6 T or less than 0.6 T

Explanation : Since μr for silicon steel is more than that of cast iron, flux density will be more than 0.6 T.

63 .
Two voltages are v1= 100 sin (ωt + 15°) and v2 = 60 cosωt, then
A)
v1 is leading v2 by 15°
B)
v2 is lagging v1 by 15°
C)
v2 is leading v1 by 75°
D)
v1 is leading v2 by 75°

Correct Answer :   v2 is leading v1 by 75°

Explaination : v1 = 100 sin (ωt + 15°) and v2 = 60 cos ωt = 60 sin (ωt + 90°). Hence, v2 is leading v1 by (90 - 15) = 75°.

64 .
An RL admittance function can also be realized as
A)
RC admittance function
B)
RC impedance function
C)
LC admittance function
D)
LC impedance function

Correct Answer :   RC impedance function

Explanation : RL admittance function and RC impedance function have similar forms.

65 .
In active filters inductances are divided because they
A)
are non linear
B)
saturate quickly
C)
are always associated with same resistance
D)
are bulky and unsuitable for miniaturization

Correct Answer :   are bulky and unsuitable for miniaturization

Explanation : Active filters consist of electronic components and have very small size.

66 .
Three resistance of 15 Ω each are connected in delta. The resistance of equivalent star will have a value of
A)
5 Ω
B)
5/3 Ω
C)
15 Ω
D)
45 Ω

Correct Answer :   5 Ω

Explanation :

67 .
The synthesis of minimum function was suggested by
A)
O'Brune
B)
R. Richards
C)
Bott and Duffin
D)
None of the above

Correct Answer :   O'Brune

Explanation : The procedure is called Brune's synthesis.

68 .
A 3 phase balanced supply feeds 3 phase unbalanced load. Power supplied to the load can be measured by using

1. 2 wattmeter
2. one wattmeter
3. 3 wattmeter

Which of the above statements is correct?
A)
1 and 2
B)
1 and 3
C)
2 and 3
D)
3 alone

Correct Answer :   1 and 3

Explaination : A minimum of 2 wattmeters is required to measure 3 phase power. Of course power can be measured by putting one wattmeter in each phase.

69 .
Which of the following is correct for a driving point functions?
A)
The real parts of all poles must be negative
B)
The real parts of all zeros must be negative
C)
The real parts of all poles and zeros must be negative
D)
The real parts of all poles and zeros must be negative or zero

Correct Answer :   The real parts of all poles and zeros must be negative or zero

Explanation : It is a necessary condition for response to be stable.

70 .
In an RC series circuit R = 100 Ω and XC = 10 Ω. In this circuit
A)
the current and voltage are in phase
B)
 
the current lags the voltage by about 6°
C)
the current leads the voltage by about 6°
D)
the current leads the voltage by about 84°

Correct Answer :   the current leads the voltage by about 6°

Explaination : In RC circuit the current leads the voltage.

71 .
A current is flowing through a conductor with non-uniform area of cross-section. Then
A)
current will be the same at all the cross-sections.
B)
current will be different at different cross-sections.
C)
current will be different but current density will be same at all the cross-sections
D)
current will be the same but current density will be different at different cross-sections.

Correct Answer :   current will be the same but current density will be different at different cross-sections.

Explanation : Current density = current/area of cross-section. Same current throughout the conductor.

Since, area of cross-section is non-uniform, current density will be different at different cross-sections.

72 .
The electrical energy required to heat a bucket of water to a certain temperature is 2 kWh. If heat losses, are 25%, the energy input is
A)
2.5 kWh
B)
2.67 kWh
C)
3 kWh
D)
3.5 kWh

Correct Answer :   2.67 kWh

Explanation : Since 25% of input is lost, 0.75 Input = 2 or input = 2/0.75 = 2.67 kWh

73 .
The current rating of a cable depends on
A)
diameter of cable
B)
length of cable
C)
both length and diameter of cable
D)
None of the above

Correct Answer :   diameter of cable

Explanation : Current rating depends only on area of cross-section and hence diameter.

74 .
In an ac circuit, the maximum and minimum values of power factor can be
A)
0 and -1
B)
1 and 0
C)
1 and -1
D)
2 and 0

Correct Answer :   1 and 0

Explanation : Power factor is maximum and equal to 1 for purely resistive load. Power factor is minimum and equal to zero for purely reactive load.

75 .
A two branch parallel circuit has a 20 Ω resistance and 1 H inductance in one branch and a 100 μF capacitor in the second branch. It is fed from 100 V ac supply, at resonance, the input impedance of the circuit is
A)
5 Ω
B)
20 Ω
C)
50 Ω
D)
500 Ω

Correct Answer :   500 Ω

Explaination : At parallel resonance circuit impedance = L/RC

76 .
As compared to the number of network elements in Brune synthesis, the number of network elements Bott-and Duffin in realization is
A)
less
B)
equal
C)
more
D)
Any of the above

Correct Answer :   more

Explanation : To avoid mutually coupled inductors, more elements are needed.

77 .
A sinusoidal voltage has peak to peak value of 100 V. The rms value is
A)
35.35 V
B)
50 V
C)
70.7 V
D)
141.41 V

Correct Answer :   35.35 V

Explanation : Peak value = 50 V, rms value = 50 / √2 = 35.35 V.

78 .
A capacitor is needed for an ac circuit of 230 V, 50 Hz the peak voltage rating of the capacitor should be
A)
230 V
B)
0.5 x 230 V
C)
√2 x 230V
D)
230/√2V

Correct Answer :   √2 x 230V

Explanation : Peak voltage rating = √2 (rms voltage rating).

79 .
Assertion (A): In an R-L circuit having high inductance, the rise of current is very slow.

Reason (R): The time constant of R-L circuit is L/R.
A)
A is true but R is false
B)
A is false but R is true
C)
Both A and R are true and R is not the correct explanation of A
D)
Both A and R are true and R is correct explanation of A

Correct Answer :   Both A and R are true and R is correct explanation of A

Explaination : A high value of time constant results in slow rise of current.

80 .
A two branch tuned circuit has a coil of resistance R and inductance L in one branch and capacitance C in the second branch. If R is increased, the dynamic resistance
A)
increases
B)
decreases
C)
remains constant
D)
may increases or decreases

Correct Answer :   decreases

Explaination : Dynamic resistance = L/RC

81 .
A constant k band pass filter has a pass band from 100 to 400 Hz. The resonant frequency of series and shunt arms is
A)
1500 Hz
B)
2000 Hz
C)
2500 Hz
D)
3000 Hz

Correct Answer :   2000 Hz

Explanation : Resonant frequency of arms in constant k band pass filter =

82 .
Two similar coupled coils are connected in series. The total inductance in series aiding connection is 100 mH. If currents is 3 A, the energy stored in magnetic field is
A)
0.9 J
B)
0.45 J
C)
0.225 J
D)
1.8 J

Correct Answer :   0.225 J

Explaination : Energy = 0.5 LI2

83 .
Thevenin's impedance of an ac network is in general
A)
Resistance
B)
R and L in series
C)
R and C in series
D)
Either R and L or R and C in series

Correct Answer :   Either R and L or R and C in series

Explanation : Thevenin's impedance may be inductive or capacitive.

84 .
The average value of the waveform is
A)
0 V
B)
2 V
C)
3 V
D)
4 V

Correct Answer :   0 V

Explaination :

85 .
An RLC series circuit has Q = 100 and ω0 = 20 rad/sec. The bandwidth is
A)
0.2 rad/sec
B)
2 rad/sec
C)
20 rad/sec
D)
2000 rad/sec

Correct Answer :   0.2 rad/sec

86 .
In an unloaded transformer, the fluxes limiting the primary and secondary are 30 mWb and 20 mWb. The coefficient of coupling is
A)
1
B)
0.1
C)
0.33
D)
0.67

Correct Answer :   0.67

Explanation :

87 .
Poles and zeros of a driving point function of a network are simple and alternate on jω axis. The network consists of
A)
R and C
B)
R and L
C)
L and C
D)
R, L and C

Correct Answer :   L and C

Explanation : In network having only L and C, poles and zeros of driving point function are simple and alternate on jω axis.

88 .
A 10 μF capacitor is charged from a 5 volt source through a resistance of 10 kΩ. The charging current offer 35 m sec. If the initial voltage on C is - 3 V is
A)
0.56 mA
B)
5 μA
C)
5.6 mA
D)
6 mA

Correct Answer :   0.56 mA

Explaination :

89 .
If an admittance Y(s) has a term Ks, the realization would give
A)
a resistance of value K
B)
an inductance of value K
C)
a capacitance of value K
D)
Either (A) or(C)

Correct Answer :   an inductance of value K

Explanation : Admittance of a capacitance K is Ks.

90 .
If the diameter of a wire is doubled, the current carrying capacity of the wire becomes
A)
half
B)
twice
C)
four times
D)
one-fourth

Correct Answer :   four times

Explanation : Since diameter is doubled, area of cross-section becomes four times. Current carrying capacity is proportional to area of cross-section.

91 .
Two voltages 50 V each have a phase difference of 45°. The rms value of resultant sum of the two voltages is
A)
70.7 V
B)
80.4 V
C)
92.4 V
D)
100 V

Correct Answer :   92.4 V

Explanation : RMS value =

92 .
The energy stored in a coil is 108 J. It is opened suddenly in 10 ms. The power dissipated instantaneously across the blades of switch is
A)
108 W
B)
1080 W
C)
10800 W
D)
108000 W

Correct Answer :   10800 W

Explanation :

93 .
A bulb rated at 60 W, 120 V is used for 30 minutes. The charge associated with this operation is
A)
600 C
B)
900 C
C)
3600 C
D)
7200 C

Correct Answer :   900 C

Explanation :

94 .
Two coil have their axis perpendicular to each other. The coefficient of coupling k is
A)
0
B)
0.5
C)
1
D)
more than 0 but less than 1

Correct Answer :   0

Explanation : When axis are perpendicular then there is no mutual coupling.

95 .
A constant k low pass T section filter has a characteristic impedance of 600 p at zero frequency. At f = fc the characteristic impedance is
A)
zero
B)
600 Ω
C)
infinite
D)
more than 600 ohms

Correct Answer :   zero

Explaination : Z0T = R0(1 - f2 / fc2)0.5. At f = f0. Z0T = 0.

96 .
A low-pass filter frequency responce H (jω) = A (ω) ejΦ(ω) does not produce any phase distortion, if
A)
A(ω) = Cω2, Φ (ω) = kω3
B)
A(ω) = Cω2, Φ (ω) = kω
C)
A(ω) = Cω2, Φ (ω) = kω2
D)
A(ω) = C, Φ (ω) = kω-1

Correct Answer :   A(ω) = Cω2, Φ (ω) = kω

97 .
In a tungsten filament lamp
A)
the current at the instant of switching is equal to operating current
B)
the current at the instant of switching is less than operating current
C)
the current at the instant of switching is more than operating current
D)
the current at the instant of switching may be less than or equal to operating current

Correct Answer :   the current at the instant of switching may be less than or equal to operating current

Explanation : Resistance at the time of switching on is minimum and increases due to increase of temperature.

98 .
Two similar mutually coupled coils have a total inductance of 900 mH and coefficient of coupling 0.5. The self inductance of each coils is
A)
300 mH
B)
150 mH
C)
75 mH
D)
50 mH

Correct Answer :   300 mH

Explanation : M = k√L1L2, L1 = L2 = L, M = kL. Total inductance = L1 + L2 + 2M = 2L + 2kL = 900 mH or L(2 + 2 x 0.5) = 900 or L = 300 mH.

99 .
The function of a choke in a fluorescent lamp is
A)
at the time of starting only
B)
during the working of time but not at starting time
C)
both at the time of starting and during working
D)
None of the above

Correct Answer :   both at the time of starting and during working

Explanation : At the time of starting the choke provides a high voltage. During working there is voltage drop across choke so that lamp gets proper voltage.

100 .
A series resonant circuit is fed by a voltage having rms value V. At resonance, the voltage across inductance VL and voltage across capacitance VC are related as
A)
VL > VC
B)
VL < VC
C)
VL = VC
D)
VL = 0.5 VC

Correct Answer :   VL = VC

Explaination : At resonance XL = XC. Therefore IXL = IXC or VL = VC.

101 .
The function Z(s) has a pole at infinity if
A)
the degree of numerator and denominator of Z(s) are equal
B)
the numerator of Z(s) is one degree higher than denominator
C)
the denominator of Z(s) is one degree higher than numerator
D)
the degree of numerator and denominator are either equal or differ by one

Correct Answer :   the numerator of Z(s) is one degree higher than denominator

Explanation : If numerator is one degree higher than denominator z(s) tends to infinity as s tends to infinity.

102 .
A thermal power plant has an efficiency of 0.4. If 0.6 kg of coal is burnt to generate 1 kWh, the calorific value of coal is
A)
about 1500 kcal/kg
B)
about 2500 kcal/kg
C)
about 3500 kcal/kg
D)
about 7500 kcal/kg

Correct Answer :   about 3500 kcal/kg

103 .
An RC series circuit has R = 20 Ω and Xc = 20 Ω. Then Z =
A)
40 Ω
B)
28.28 Ω
C)
20 Ω
D)
1 Ω

Correct Answer :   28.28 Ω

104 .
An inductance having XL = 5 Ω and a capacitance having XC = 5 Ω are connected in parallel across 100 V, 50 Hz supply. The current drawn from source is
A)
zero
B)
20 A
C)
28.28 A
D)
40 A

Correct Answer :   zero

105 .
Assertion (A) : Millman's theorem helps in replacing a number of current sources in parallel by a single current source.

Reason (R) : Maximum power transfer theorem is applicable only for dc, circuits.
A)
A is false but R is true
B)
A is true but R is false
C)
Both A and R are true and R is correct explanation of A
D)
Both A and R are true and R is not the correct explanation of A

Correct Answer :   A is true but R is false

Explaination : Maximum power transfer theorem is applicable to ac circuits.

106 .
In a series RLC circuit the phase angle θ of impedance Z ∠θ is positive. The circuit will behave as
A)
RC circuit
B)
RL circuit
C)
resistive circuit
D)
Either RL or RC circuit

Correct Answer :   RC circuit

Explanation : In RL circuits phase angle of Z is positive.

107 .
In a two terminals network the O.C. voltage measured at the given terminals is 100 V and s.c., currents at the same terminals 5 A. If a load of 80 Ω resistance is connected at the terminals, load current is
A)
1 A
B)
1.25 A
C)
6 A
D)
6.25 A

Correct Answer :   1 A

Explaination :

108 .
A coil has resistance R and inductance L. At ω = ∞ the phase angle between voltage and current is
A)
0°
B)
45°
C)
90°
D)
180°

Correct Answer :   90°

Explanation :

109 .
Double integration of unit step function leads to
A)
a ramp
B)
a doublet
C)
an impulse
D)
a parabola

Correct Answer :   a parabola

Explanation : Integral of unit step function is ramp and integral of ramp is doublet.

110 .
A conductor has a cylindrical shape with a diameter d. Its resistance is 2 Ω. It is recast into a cylindrical conductor of diameter 0.3d. The resistance of new conductor is likely to be
A)
less than 2 Ω
B)
less than 0.6 Ω
C)
between 2 and 100 Ω
D)
more than 100 Ω

Correct Answer :   more than 100 Ω

Explanation :

111 .
One commercial unit of energy is equal to
A)
1 watt-sec
B)
1 kilowatt-sec
C)
1 kilowatt-hour
D)
One watt-hour

Correct Answer :   1 kilowatt-hour

Explanation : Consumers are charged on the basis of kWh of energy used.

112 .
Two coupled coils with self inductances of 4 mH and 16 mH are connected in series. The maximum possible value of inductance can be
A)
20 mH
B)
28 mH
C)
36 mH
D)
64 mH

Correct Answer :   36 mH

Explanation :

113 .
A resistor is rated at 0.75 watt, 1 kΩ. Its current rating is
A)
1 mA
B)
1.268 mA
C)
5.393 mA
D)
27.386 mA

Correct Answer :   27.386 mA

Explanation : 0.75 = I2 x 1 x 1000 or I = 27.386 mA.

114 .
If P = 250 W and p.f. = 0.707 lagging, Q =
A)
- 250 vars
B)
250 vars
C)
- 176.75 vars
D)
176.7 vars

Correct Answer :   250 vars

Explanation :

Apparent power = , Q = 250 vars and lagging vars are taken as positive.

115 .
A series RLC circuit is at resonance at 200 Hz. If capacitance is increased to four times, the circuit will be in resonance at
A)
100 Hz
B)
200 Hz
C)
400 Hz
D)
800 Hz

Correct Answer :   100 Hz

116 .
The temperature coefficient of copper is 0.00393 at 20° C. At 50° C the temperature coefficient is
A)
0.0015
B)
0.0025
C)
0.0035
D)
0.0042

Correct Answer :   0.0035

117 .
To determine the polarity of voltage drop across a resistor, it is sufficient to know
A)
direction of current through the resistor
B)
magnitude of current through the resistance
C)
direction and magnitude of current through the resistor
D)
direction and magnitude of current and value of resistance

Correct Answer :   direction of current through the resistor

Explanation : Polarity of voltage depends only on direction of current and nothing else.

118 .
A sawtooth current wave is passed through a resistance
A)
the waveshape of power will be sawtooth
B)
the waveshape of voltage across resistance will be sawtooth
C)
neither the voltage waveshape nor power wave-shape will be sawtooth
D)
the waveshapes of voltages across resistance and power will also the sawtooth

Correct Answer :   the waveshape of voltage across resistance will be sawtooth

Explanation : V = IR and P = I2R. Therefore, waveshape of V is the same as that of I but waveshape of P is different.

119 .
The three sides of an admittance triangle denote
A)
R, X, Y
B)
G, B, Y
C)
G, B, Z
D)
(R, Y, Z) or (R, X, Z)

Correct Answer :   (R, Y, Z) or (R, X, Z)

Explanation : Admittance triangle depicts admittance Y and its components G and B.

120 .
A step voltage E is applied to an R-L series circuit. At t = 0, the current in the circuit is
A)
zero
B)
infinity
C)
E/L
D)
E/R

Correct Answer :   zero

Explanation : Inductance does not allow the current to increase instantaneously.

121 .
To find current in a resistance connected in a network, Thevenin's theorem is used VTH = 20 V and RTH = 5 Ω. The current through the resistance
A)
is 4 A
B)
is 4 A or less
C)
is less than 4 A
D)
may be 4 A or less or more than 4 A

Correct Answer :   is less than 4 A

122 .
A step voltage E is applied to a series R-L circuit. The rate of change of current is maximum at t =
A)
zero
B)
L/R
C)
R/L
D)
infinity

Correct Answer :   zero

Explanation :

123 .
The total inductance of two coils is 60 mH in series aiding connection and 40 mH in series opposing connection. The mutual inductance between coils is
A)
2.5 mH
B)
5 mH
C)
10 mH
D)
20 mH

Correct Answer :   5 mH

124 .
An RC circuit initially at rest has a step signal. The response V(t) across C is V(t) = 1 - e-at, If now there is an initial voltage on C of 2 volts for the same step signal, V(t) is now
A)
 
1 + e -at
B)
 
1 + 2e -at
C)
2 - e -at
D)
3 - e -at

Correct Answer :  

 
1 + e -at

Explaination :

125 .
An R-L series circuit has R = 5 Ω and L = .01 H. It is fed by ac 50 Hz supply. The rms current in the circuit is 5 A. The active power supplied by the source is
A)
 
25 W
B)
 
50 W
C)
125 W
D)
250 W

Correct Answer :   125 W

Explaination : P = I2R = 52(5) = 125 W.

126 .
A particular current is made up of two components 10A dc and sinusoidal current of peak value 14.14A. The average of resultant current is
A)
zero
B)
10A
C)
14.14A
D)
24.14A

Correct Answer :   10A

Explanation : The average of sinusoid over 1 cycle is zero.

127 .
Assertion (A): In series R-L-C circuit, the current may lead or lag the voltage depending on the value of R.

Reason (R): Phase angle of an R-L series circuit is tan-1 (ωL/R).
A)
A is false but R is true
B)
A is true but R is false
C)
Both A and R are true and R is correct explanation of A
D)
Both A and R are true and R is not the correct explanation of A

Correct Answer :   A is false but R is true

Explaination : The current may lead or lag the voltage depending on values of L and C.

128 .
An RL impedance function can also be realized as
A)
LC impedance function
B)
LC admittance function
C)
RC impedance function
D)
RC admittance function

Correct Answer :   RC admittance function

Explanation : RL impedance function and RC admittance have similar forms.

129 .
A step voltages is applied to RLC series circuit having R = 2 Ω, L = 1 H and C = 1 F. The transient current response will be
A)
over damped
B)
under damped
C)
critically damped
D)
any of the above depending the magnitude of voltage

Correct Answer :   critically damped

130 .
An RLC series circuit has R = 30 Ω, XL = 30 Ω and XC = 30 W. Its impedance is
A)
30 ∠0°.
B)
30 ∠45°
C)
42.42 ∠45°
D)
90 ∠45°.

Correct Answer :   30 ∠0°.

Explaination : Z = 30 + j (30 - 30) = 30∠0 Ω.

131 .
In a 3 phase system, the zero sequence component of line to line voltages is zero
A)
if line to line voltages are balanced
B)
if line to line voltages are unbalanced
C)
if line to line voltages are balanced or unbalanced
D)
if degree of unbalanced in line to line voltages is small

Correct Answer :   if line to line voltages are balanced or unbalanced

Explanation : Zero sequence component of line to line voltage is always zero irrespective of degree of unbalance.

132 .
For a nonlinear resistance
A)
v-i plot is not a straight line
B)
current decreases as voltage increases
C)
resistance increases as current increases
D)
resistance decreases as current increases

Correct Answer :   v-i plot is not a straight line

Explanation : In a non-linear resistance v-i graph is a curve.

133 .
The current through a 10 Ω resistance in a dc circuit having two emf sources is 3A. If this resistance is changed to 20 Ω, the new value of current will be
A)
1.5 A
B)
less than 3 A
C)
equal or less than 3 A
D)
equal to or less or more than 3 A

Correct Answer :   less than 3 A

Explanation : The current will be less than 3 A. It may not be 1.5 A because other resistance in the circuit also affect the value of current.

134 .
A planar graph has 6 nodes and 7 branches. The number of meshes in the dual graph is
A)
2
B)
3
C)
4
D)
6

Correct Answer :   2

Explanation : In dual, node pairs and meshes are interchanged b = (n - 1) + l => l = 2.

135 .
An ac voltage 20 sin 1000t feeds an R-C series circuit. R = 8 Ω and active power is 4 W. The power factor is
A)
1
B)
0.4
C)
0.6
D)
0.8

Correct Answer :   0.4

Explanation :

136 .
The poles and zeros of a positive real function
A)
may lie any where in s plane
B)
must occur in conjugate pair
C)
may have positive or negative real part
D)
must have either negative or zero real part

Correct Answer :   must have either negative or zero real part

Explanation : Only then it is possible to synthesize by R, L and C elements.

137 .
Two resistances of 2 Ω each are connected in series. A shunt having zero resistance is connected across the combination. The overall resistance will be
A)
1 Ω
B)
4 Ω
C)
zero
D)
0.5 Ω

Correct Answer :   zero

Explanation :

138 .
In a linear circuit, the superposition principle can be applied to calculate the
A)
voltage and power
B)
current and power
C)
voltage and current
D)
voltage, current and power

Correct Answer :   voltage and current

Explanation :

139 .
The output voltage of a charger is
A)
same as battery voltage
B)
more than battery voltage
C)
less than battery voltage
D)
same or more than battery voltage

Correct Answer :   more than battery voltage

Explanation : The charger has to supply current to battery for charging. This is possible only if voltage of charger is more than that of battery.

140 .
Maximum power transfer theorem finds application in
A)
communication circuits
B)
power circuits
C)
distribution circuits
D)
both power and communication circuits

Correct Answer :   communication circuits

Explanation : In power and distribution circuits efficiency has to be very high.

141 .
In a series L-C circuit fed by ac voltage, voltage drops across L and C are 40 V and 30 V respectively. The supply voltage is
A)
10 V
B)
50 V
C)
70 V
D)
1.333 V

Correct Answer :   50 V

Explanation : |V| = IXL - IXC.

142 .
In a reactance function
A)
all poles are simple
B)
all poles and zeros are simple
C)
all poles and zeros lie on negative real axis
D)
all poles and zeros are simple and lie on jω axis only

Correct Answer :   all poles and zeros are simple and lie on jω axis only

Explanation : Only then the network has only L and C. If poles and zeros are not on jω axis, resistance will be there.

143 .
If f(t) = - f(- t) and f(t) satisfies Dirichlet conditions, then f(t) can be expanded in Fourier series having
A)
sine terms only
B)
cosine terms only
C)
sine and constant term
D)
cosine and constant terms

Correct Answer :   sine terms only

Explanation : Since f(-t) = -f(t) only sine terms exist.

144 .
If A = 3 + j1 and B = 4 + j3, A - B =
A)
 
10 ∠45°
B)
8.062 ∠29.7°
C)
2.236 ∠243.43°
D)
6.72 ∠243.43°

Correct Answer :   2.236 ∠243.43°

Explaination : A - B = - 1 - j2 = 2.236∠243.43°.

145 .
Two capacitors of 20 μF each are in series. The total capacitance is
A)
5 μF
B)
10 μF
C)
40 μF
D)
400 μF

Correct Answer :   10 μF

Explanation :

146 .
Thevenin's theorem is used to find current in a branch of a network. It is now desired to find current in another branch of the network
A)
the same Thevenin's circuit can be used
B)
it is necessary to find new Thevenin's circuit
C)
the same Thevenin's circuit with some modification can be used
D)
None of the above

Correct Answer :   it is necessary to find new Thevenin's circuit

Explanation : Thevenin's equivalent circuit with respect to particular terminals only.

147 .
A series resonant circuit has R = 2 Ω, L = 0.1 H and C =10 μF. At resonance applied voltage = 10 ∠0 V. Voltage across inductance is likely to be
A)
 
10 ∠0 V
B)
10 ∠45° V
C)
100 ∠90° V
D)
100 ∠-90° V

Correct Answer :   100 ∠90° V

Explaination : Voltage across inductance = QV and leads the applied voltage.

148 .
Two phasors having rms values V1 and V2 which are added to give a phasor having rms value V3. V3 is maximum if phase angle between V1 and V2 is
A)
 
90°
B)
 
180°
C)
 
270°
D)
 
360°

Correct Answer :  

 
360°

Explaination : Sum of phasors is maximum if they are in phase and 360° = 0.

149 .
If e = 110 sin (ωt + p/3) and i = 5 sin (ωt - p/3), the impedance of the circuit is
A)
 
11 Ω
B)
16 Ω
C)
22 Ω
D)
30.8 Ω

Correct Answer :   22 Ω

Explaination :

150 .
Ohm's law is valid for
A)
dc voltage and current
B)
ac voltage and current
C)
dc and ac voltages and currents
D)
all voltages and current

Correct Answer :   all voltages and current

Explanation : KCL and KVL are valid for voltages and currents of all wave shapes during transient as well as steady state conductions.