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MCQ தேர்வு
Q1
An overexcited synchronous motor operates at:
A
Lagging power factor
B
Unity power factor only
C
Leading power factor
D
Zero power factor always
Q2
Which logic family generally offers the lowest static power dissipation?
A
ECL
B
TTL
C
CMOS
D
RTL
Q3
For a three-phase balanced star-connected load, if the phase voltage is 230 V, what is the line voltage?
A
230 V
B
398.4 V
C
460 V
D
690 V
Q4
In a capacitor-input filter, increasing the capacitance generally causes the ripple voltage to:
A
Increase
B
Decrease
C
Remain unchanged
D
Become zero always
Q5
Which relay is commonly used for protection of long high-voltage transmission lines?
A
Thermal relay
B
Distance relay
C
Overload relay only
D
Buchholz relay
Q6
For an ideal op-amp operating with negative feedback, the voltage difference between its input terminals is approximately:
A
Infinite
B
Equal to supply voltage
C
Zero
D
Equal to output voltage
Q7
For maximum power transfer in an AC circuit, the load impedance should be:
A
Equal to source impedance
B
Conjugate of source impedance
C
Twice source impedance
D
Half the source impedance
Q8
The skin effect in a conductor causes:
A
Current to concentrate at the surface at AC
B
Current to concentrate at the center at AC
C
Resistance to become zero
D
Inductance to become zero
Q9
The quality factor of a series RLC circuit at resonance is:
A
R/(ω0L)
B
ω0L/R
C
1/(ω0LR)
D
ω0R/L
Q10
The cogging phenomenon in an induction motor occurs mainly due to:
A
Rotor overheating
B
Magnetic locking between stator and rotor teeth
C
Low rotor resistance
D
Excessive slip only
Q11
The crawling phenomenon in an induction motor is mainly associated with:
A
Fundamental harmonic
B
Seventh harmonic
C
Third harmonic only
D
DC component
Q12
Which starting method provides the highest starting torque for a slip-ring induction motor?
A
Direct-on-line starting
B
Star-delta starting
C
Rotor resistance starting
D
Autotransformer starting
Q13
The synchronous speed of a 6-pole, 50 Hz induction motor is:
A
500 rpm
B
750 rpm
C
1000 rpm
D
1500 rpm
Q14
The rotor frequency of an induction motor operating at slip s and supply frequency f is:
A
f/s
B
f(1−s)
C
sf
D
f+s
Q15
The slip of an induction motor operating at 1440 rpm on a 50 Hz, four-pole supply is:
A
2%
B
4%
C
6%
D
8%
Q16
Aliasing in an ADC occurs when the sampling frequency is:
A
Greater than twice the highest input frequency
B
Exactly zero
C
Less than twice the highest input frequency
D
Infinite
Q17
In a MOSFET, the gate current under steady-state DC operation is ideally:
A
Very large
B
Approximately zero
C
Equal to drain current
D
Equal to source current
Q18
PWM inverters are primarily used to:
A
Eliminate all switching losses
B
Control output voltage and reduce selected harmonics
C
Convert AC directly into DC
D
Increase transformer core loss
Q19
The main purpose of earthing electrical equipment is to:
A
Increase load current
B
Provide a low-impedance path for fault current and limit touch voltage
C
Increase supply voltage
D
Improve motor speed
Q20
In a balanced Wheatstone bridge, the galvanometer current is:
A
Maximum
B
Zero
C
Equal to supply current
D
Infinite
Q21
The ripple frequency of a three-phase full-wave bridge rectifier supplied from a 50 Hz source is:
A
50 Hz
B
100 Hz
C
150 Hz
D
300 Hz
Q22
In a DC shunt motor, which condition primarily causes the motor speed to increase dangerously?
A
Increase in armature resistance
B
Open-circuit field winding
C
Increase in load
D
Decrease in armature voltage
Q23
In a power system, the primary purpose of reactive power compensation using shunt capacitors is to:
A
Increase line current
B
Improve power factor and reduce reactive current
C
Increase system frequency
D
Increase transformer copper loss
Q24
A 10 kVA, 200/400 V transformer has a full-load secondary current of:
A
12.5 A
B
25 A
C
50 A
D
100 A
Q25
A CT secondary should never be open-circuited while its primary is energized because:
A
Primary current becomes zero
B
Dangerously high secondary voltage may develop
C
Frequency becomes zero
D
The CT becomes a capacitor
Q26
For an ideal boost converter operating in continuous conduction mode, the output voltage is:
A
DVd
B
Vd(1−D)
C
Vd/(1−D)
D
VdD/(1−D)
Q27
For a symmetrical three-phase fault, the negative and zero sequence currents are:
A
Equal to positive sequence current
B
Zero
C
Twice positive sequence current
D
Infinite
Q28
The condition for maximum power transfer from a DC source to a resistive load is:
A
RL = 0
B
RL = Rth
C
RL = 2Rth
D
RL = ∞
Q29
Which test on a transformer is primarily used to determine core loss?
A
Short-circuit test
B
Open-circuit test
C
Load test
D
Sumpner test only
Q30
The resolution of an ideal n-bit ADC expressed as a fraction of full-scale range is approximately:
A
1/n
B
1/2^n
C
2^n
D
n/2
Q31
In a synchronous generator, the frequency of generated emf is determined primarily by:
A
Rotor resistance
B
Excitation current only
C
Speed and number of poles
D
Armature resistance
Q32
A 50 Hz transformer has a maximum flux of 0.01 Wb and 100 turns in its primary winding. What is the approximate RMS induced emf?
A
222 V
B
314 V
C
444 V
D
628 V
Q33
In a transformer, the maximum efficiency occurs when:
A
Copper loss is zero
B
Iron loss is zero
C
Copper loss equals iron loss
D
Copper loss is twice iron loss
Q34
Which motor is preferred where high starting torque and variable speed are required?
A
DC series motor
B
DC shunt motor
C
Synchronous motor
D
Reluctance motor
Q35
The primary function of a circuit breaker is to:
A
Measure voltage
B
Interrupt fault current
C
Improve power factor
D
Generate electrical power
Q36
The Ferranti effect becomes significant in:
A
Short loaded lines
B
Long lightly loaded or unloaded lines
C
DC transmission lines
D
Low-voltage cables only
Q37
For a single line-to-ground fault, the positive, negative and zero sequence networks are connected:
A
In parallel
B
Only positive sequence
C
In series
D
Only zero sequence
Q38
In a DC machine, armature reaction mainly causes:
A
Only mechanical losses
B
Flux distortion and weakening
C
Increase in insulation resistance
D
Reduction in brush contact resistance
Q39
Bundled conductors in EHV transmission lines are mainly used to:
A
Increase corona loss
B
Reduce corona and increase power-transfer capability
C
Increase conductor resistance
D
Reduce mechanical strength
Q40
A common-emitter BJT amplifier provides a phase shift between input and output of approximately:
A
0°
B
90°
C
180°
D
270°
Q41
In a buck converter operating in continuous conduction mode, the ideal output voltage is:
A
Vd/(1−D)
B
DVd
C
Vd/D
D
(1−D)Vd
Q42
For an overhead transmission line, corona loss increases significantly with:
A
Decrease in conductor diameter
B
Increase in air density
C
Increase in operating voltage
D
Decrease in conductor spacing
Q43
Which power electronic device can be turned OFF by a gate signal under normal operation?
A
SCR
B
TRIAC
C
GTO
D
DIAC
Q44
A three-phase induction motor draws 20 A at 0.8 power factor from a 400 V supply. Its approximate active input power is:
A
8.32 kW
B
11.09 kW
C
13.86 kW
D
16.00 kW
Q45
The reach of a distance relay is primarily determined by:
A
Measured impedance
B
Transformer oil level
C
Generator speed
D
Frequency alone
Q46
The characteristic impedance of a lossless transmission line is determined by:
A
Only line length
B
L/C ratio
C
R/G ratio
D
Only load resistance
Q47
In a DC generator, the commutator primarily acts as:
A
A voltage regulator
B
A mechanical rectifier
C
A current amplifier
D
A frequency converter
Q48
The primary purpose of the Buchholz relay in an oil-immersed transformer is to detect:
A
External short circuits only
B
Internal faults producing gas
C
Overvoltage only
D
Low oil temperature
Q49
Which semiconductor material has the widest band gap among the following?
A
Germanium
B
Silicon
C
Gallium arsenide
D
Indium antimonide
Q50
A DC series motor should never be operated without mechanical load because:
A
Its torque becomes zero
B
It may attain dangerously high speed
C
Its field current becomes infinite
D
Its armature resistance becomes zero
Q51
In a phase-locked loop, the VCO frequency is controlled by:
A
Input resistance only
B
Control voltage
C
Output impedance only
D
Transformer turns ratio
Q52
The per-unit impedance of a transformer is independent of:
A
Choice of base MVA
B
Choice of base voltage
C
Actual transformer rating
D
Both base MVA and base voltage
Q53
The power factor of a synchronous motor can be controlled by varying its:
A
Mechanical load only
B
Supply frequency only
C
Field excitation
D
Armature resistance
Q54
The Barkhausen criterion for sustained oscillation requires the loop gain to satisfy:
A
|Aβ| = 0
B
|Aβ| < 1
C
|Aβ| = 1 with net phase shift 0° or 360°
D
|Aβ| > 100 always
Q55
At resonance in a series RLC circuit, the impedance is:
A
Maximum and purely inductive
B
Minimum and purely resistive
C
Maximum and purely capacitive
D
Zero for every practical circuit
Q56
In an ideal voltage-source inverter, the output voltage waveform is fundamentally controlled by:
A
Only load resistance
B
Switching strategy and DC-link voltage
C
Transformer oil temperature
D
Rotor slip
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