Correct Answer: D
Explanation:
Explanation:
Field?Effect Transistors are voltage?controlled devices (gate voltage controls channel current).
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1. FET belongs to which of the following type of device?
A
Current controlled device
B
Magnetic device
C
Power controlled device
D
Voltage controlled device
Field?Effect Transistors are voltage?controlled devices (gate voltage controls channel current).
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2. What is the purpose of providing a fuse in an electric circuit?
A
To safe guard the installation against heavy current
B
To reduce the current flowing in the circuit
C
To reduce the power consumption
D
To improve power factor
Fuses protect circuits from excessive current by blowing when current exceeds rating.
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3. Which among the following is the dual of Boolean expression X+YZ=(X+Y) (X+Z)?
A
X(Y+Z)=XY+YZ
B
X.(Y+Z)=X.Y+X.Z
C
X+(Y+Z) = X.Y+Z
D
X+(YZ) = X+Y+Z
Dual of distribution law X+YZ = (X+Y)(X+Z) is X(Y+Z)=XY+XZ (option B with corrected formatting).
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4. A three phase transmission line delivers a load of 5 MW at 0.8 power factor lagging. Resistance of each conductor is 0.5 ohm / km. Receiving end voltage is 33 kV. If the line loss is not to exceed 10%, determine the length of the line.
A
7 km
B
27.9 km
C
56.8 km
D
13.9 km
Computed I = 109.35 A and required length L ? 27.878 km to keep losses ?10% (see Excel). Choose nearest option if desired. Computed I=109.35 A, required length ? 27.878 km; nearest option B (27.9 km).
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5. One 200 KVA transformer has an iron loss of 1 KW and full load Cu loss of 2 KW. Its load KVA corresponding to maximum efficiency is:
A
100 KVA
B
141.4 KVA
C
50 KVA
D
200 KVA
Max efficiency occurs at load = rating ? sqrt(P_core/P_cu_full) =200?sqrt(1/2)=200?0.7071=141.4 KVA.
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6. In which type of the faults given below, all of the three components Ia0, Ia1 and Ia2 are equal?
A
Single line to ground fault
B
Double line to ground fault
C
Line to line fault
D
3 phase faults
For single line-to-ground fault, sequence currents are equal (Ia0=Ia1=Ia2).
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7. What does the region around the stationary electric charge has?
A
Electric field
B
Magnetic field
C
Semi permeable region
D
Insulating field
A stationary charge produces an electric field.
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8. The hysteresis loop of magnetic material has an area of 5 cm2 with the scales given as 1 cm=2AT and 1 cm=50 mWb, at 50 Hz, the total hysteresis loss is
A
15 W
B
20 W
C
25 W
D
50 W
Energy per cycle ? area ? scale factors =5?(2?0.05)=0.5 J per cycle; ?50 Hz =25 W.
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9. RMS value of rectangular wave of period T, having a value of +V for a duration T1(
A
V
B
T1-T2 / T
C
V / ?2
D
T1 /T2
Since waveform magnitude is ?V, squared value is V^2 for entire period ? RMS = V.
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10. Determine the transformer tap ratios when the receiving end voltage is equal to the sending end voltage, the high voltage line operates at 220 kV and transmit 80 MW at 0.8 pf and the impedance of the line is (40+j140)ohm. Assume tstr=1.0
A
0.8
B
0.9
C
0.7
D
0.6
Using approximate regulation/tap calculations the nearest tap ratio is 0.9 (exam-type choice).
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11. Which of the following gate is inverted OR gate?
A
NAND
B
NOR
C
AND
D
EX-OR
NOR is the inverted OR gate.
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12. What is the power factor of a cable of loss angle ????
A
sin ?
B
cos ?
C
tan ?
D
Independent of ?
Power factor = cos(loss angle).
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13. The phase voltages across a certain load are given as Va = (176 - j132) V, Vb = (-128-j96) V and Vc = (-160 +j100) V. Compute positive sequence component of voltage.
A
0
B
163.24-j35.1 V
C
50.1-j53.9 V
D
25.1-j53.9 V
Computed positive-sequence V1 = 163.25-35.43j V; choose the matching option. Computed V1 = 163.25 - j35.43 V.
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14. Which of the following serves as donor impurity in Silicon?
A
Boron
B
Indium
C
Germanium
D
Antimony
Group V element antimony acts as donor impurity in silicon (n-type).
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15. Which of the following plants is suitable for peak load?
A
Diesel engine plant
B
Steam power plant
C
Nuclear power plant
D
Hydro-electric plant
Diesel/gas turbine plants are quick-start and suitable for peak loads.
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16. What is the main drawback of the underground transmission system compared to the overhead transmission system?
A
Exposure to lightning
B
Heavy initial cost
C
Exposure to atmospheric hazards such as smoke, ice, wind
D
Induction interference between power and communication circuits
Underground cables have substantially higher installation (initial) cost.
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17. What is the pitch factor of a 4 pole alternator having 36 slots and a coil span of 1 to 8?
A
140?
B
80?
C
20?
D
40?
Coil span =7 slots; pole pitch = slots/pole =36/4=9 slots. Electrical span = (7/9)?180? ?140?.
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18. The stator of a 3 phase, 10 pole induction motor possesses 120 slots. If a lap winding is used, calculate the coil pitch, if the coil width extends from slot 1 to slot 11.
A
72.12%
B
83.30%
C
12%
D
42%
Slots per pole = 120/10 =12. Full pitch =12 slots; coil span = 11-1 =10 slots ? coil pitch =10/12 = 0.8333 =83.33%.
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19. What is the minimum clearance of HV Lines from ground across streets?
A
3 meters
B
8 meters
C
6 meters
D
5 meters
Typical minimum clearance over roads is about 6 m (varies by code).
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20. A three phase breaker is rated at 2000 MVA, 33 kV, its making current is
A
70 kA
B
89 kA
C
49 kA
D
35 kA
I = S/(?3 V) = 2000e6/(?3?33e3) ? 35 kA.
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21. Three single phase transformers are connected in delta-delta to step down a line voltage of 138 kV to 4160 V to supply power to a production plant. The plant draws 21 MW at a lagging power factor of 86 %. Calculate the apparent power furnished by the HV line.
A
24.4 MVA
B
48.8 MVA
C
12.2 MVA
D
6.1 MVA
Apparent S = P/pf = 21/0.86 ? 24.42 MVA.
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22. A 1mA D' Arsonval movement has resistance of 100 ?. It is to be converted to a 10 V voltmeter. The value of multiplier resistance is
A
999 ?
B
9999 ?
C
9900 ?
D
990 ?
Meter drop = I?R =0.001?100=0.1 V. R_mult=(10-0.1)/0.001=9900 ?.
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23. A coil having 90 turns is connected to a 120 V, 60 Hz source. If the effective value of the magnetizing current is 4 A. Calculate the inductance of the coil.
A
79.6 mH
B
121.2 mH
C
32.2 mH
D
83.16 mH
X_L = V/I = 120/4 = 30 ?. L = X/(2?f) = 30/(2??60) ? 0.0796 H = 79.6 mH.
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24. A Reactor having an inductive reactance of 4 ohm is connected to the terminals of a 120 V AC generator. Calculate the power associated with the reactor.
A
3.6 kvar
B
30 kvar
C
7.2 kvar
D
4.16 kvar
Reactive power Q = V^2 / X = 120^2 / 4 = 3600 VAR = 3.6 kVAR.
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25. What is the value of total electric flux coming out of closed surface?
A
Zero
B
Equal to volume charge density
C
Equal to the total charge enclosed by the surface
D
Equal to the surface charge density
By Gauss's law net flux through closed surface = total enclosed charge (divided by ?0 in SI, but option C best matches).
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26. A 220 kV, 3 phase transmission line is 60 km long. The resistance is 0.15 ohm / km and the inductance is 1.4 mH / km. Use the short line model to find the power at the sending end when the line is supplying a three phase load of 300 MVA at 0.8 pf lagging at 220 kV.
A
5.58MW
B
80MW
C
85.58MW
D
74.42 MW
Using short-line model and I = S/(?3 V), compute I and line losses: R_total=9 ?, I?787 A, 3I^2R ?16.7 MW so sending end power ?316.7 MW. None of the given options match; marked N/A.
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27. Which of the following power plants involves high initial cost in erecting?
A
Hydro-electric power plant
B
Steam power plant
C
Gas turbine power plant
D
Nuclear power plant
Nuclear plants have very high capital cost; hydro is also high but nuclear is typically highest.
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28. The sending and receiving end voltages of a three phase transmission line at 100 MW load are equal at 230 KV. The phase line impedance is j14 ohm. Calculate the maximum steady state power that can be transmitted over the line.
A
3778.5 MW
B
2234.56 MW
C
1784.19 MW
D
512.37 MW
Using P_max = 3*V_phase^2 / X with V_phase=230k/?3 gives ? 3.778?10^9 W (?3778.5 MW).
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29. What is the decimal equivalent of hexadecimal no (8A6)?
A
1422
B
1242
C
2122
D
2214
8A6_hex = 8*256 + 10*16 +6 = 2048 + 160 + 6 = 2214.
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30. A metal oxide varistor (MOV) is used for protecting:
A
Gate circuit against over currents
B
Gate circuit against over voltages.
C
Anode circuit against over currents.
D
Anode circuit against over voltages.
MOVs are surge arrestors protecting circuits from over-voltages.
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31. For a two port network to be reciprocal:
A
Z11= Z22
B
Y21 = Y21
C
h21 = h22
D
AD-BC = 0
Reciprocity condition depends on parameter set: e.g., for ABCD parameters AD-BC = 1. None of the provided options is correct as written.
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32. What type of excitation is given to the rotor winding of a synchronous motor?
A
DC supply at 100 -250 V
B
AC supply at 400 V
C
Revolving field
D
Induction from stator currents
Synchronous rotor is given DC excitation via slip rings/rectifier.
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33. A conductor is composed of seven identical copper strands, each having a radius 'R'. Then what is self GMD (Geometric Mean Distance) of the conductor?
A
2.645 R
B
2.177 R
C
2.141 R
D
1.21 R
Standard result for a 7?strand conductor (hexagonal close) gives GMD ? 2.141 R.
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34. To Charge a 120 V battery from a 600 V DC source using a DC chopper, The average battery current should be 20 A, with a peak to peak ripple of 2 A. If the chopper frequency is 200 Hz, calculate the duty cycle.
A
0.2
B
0.1
C
0.5
D
0.6
For step-down chopper Vb = D ? Vs ? D = 120/600 = 0.2; choose option A.
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35. A shunt motor rotating at 1500 r/min is fed by a 120 V source. The line current is 51 A and the shunt field resistance is 120 ohm. If the armature resistance is 0.1 ohm, calculate the current in the armature.
A
1 A
B
51 A
C
50 A
D
12 A
Field current = 120/120 =1 A. Armature current = total - field = 51-1 = 50 A.
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