Fundamental of Electrical Engineering MCQs with answers for all electrical related test preparation online.
Fundamental of Electrical Engineering MCQs
TRIAC is a semiconductor power electronic device which contains:
A. Two SCR’s connected in reverse parallel
B. Two SCR’s connected in parallel
C. Two SCR’s connected in series
D. Two BJT’s connected in series
An SCR can be used:
A. as static conductor
B. for power control
C. for speed control of dc shunt motor
D. All of these
Bidirectional semiconductor device is:
A. Diode
B. BJT
C. SCR
D. TRIAC
A full wave rectifier with resistive load produces:
A. Second harmonic
B. Third harmonic
C. Fifth harmonic
D. Do not produce harmonics
An ideal diode is:
A. Unidirectional
B. Bidirectional
C. Fixed voltage polarity
D. Only (a) and (c)
The IGBT resulted in higher switching speed and lower energy losses. It can be used for:
A. Uninterruptible power supplies
B. Induction heating system
C. Constant voltage and frequency power supplies
D. All of these
Harmonics in 3 phase inverters can be reduced by using:
A. Passive filter
B. Active filter
C. Both passive and active filters
D. None of these
The on – state voltage drop of IGBT consists of:
A. Drop across the collector junction
B. Drop across the drift region
C. Drop across MOSFET portion
D. All of these
The maximum firing angle in the half wave controlled regulator is:
A. 180 degree
B. 190 degree
C. 200 degree
D. 210 degree
The power MOSFET device is a:
A. Current controlled unipolar device
B. Voltage controlled unipolar device
C. Current controlled bipolar device
D. Voltage controlled bipolar device
To detect an over – current fault condition, the most reliable method is to connect a:
A. Current sensor across IGBT
B. Voltage sensor across IGBT
C. Current sensor in series with IGBT
D. Voltage sensor in series with IGBT
The conduction losses in IGBT is:
A. More than that of MOSFET
B. Lower than that of MOSFET
C. Equal to that of MOSFET
D. Equal to that of BJT
In rectifiers, load current flow is:
A. Unidirectional
B. Bidirectional
C. Either (a) or (b)
D. Non directional
Single phase VSI are mainly used in:
A. Power supplies
B. Ups
C. Multilevel configuration
D. All of these
The man made noise sources is / are:
A. Motors
B. Switches, radio interferences
C. Computers, digital electronics
D. All of these
Any electrical signal present in a circuit other than the desired signal is known as:
A. Noise
B. Distortion
C. Interference
D. All of these
In single phase VSI, the harmonic which is not present is:
A. 2nd
B. 3rd
C. 5th
D. 7th
In commutation PAC stands for:
A. Permanent angle converter
B. Phase angle converter
C. Phase angle commutation
D. Phase and commutation
Double fourier series analysis of PWM is:
A. Two dimensional functions
B. Three dimensional functions
C. One dimensional functions
D. All of these
Double edge modulation eliminates certain harmonics when the reference is a:
A. Sine wave
B. Square wave
C. Triangular wave
D. Trapezoidal wave
Under harmonic free load voltages, the 3 phase VSI:
A. Does not contains second harmonic
B. Does not contains third harmonic
C. Does not contains fifth harmonic
D. Does not contains seventh harmonic
The carrier which are commonly used in constant – frequency PWM is:
A. Sawtooth carrier
B. Inverted sawtooth carrier
C. Triangle carrier
D. All of these
In a three phase converter, the number of notches per cycle is:
A. One
B. Three
C. Six
D. Nine
The control method used for PWM dc – dc converter is:
A. Voltage mode control
B. Current mode control
C. Hysteric control
D. All of these
Between the incoming and outgoing devices in voltage commutation:
A. Large overlapping takes place
B. Small overlapping operation
C. No overlapping operation
D. None of these
The average value of the output voltage in a step – down dc chopper is given by:
A. V 0 = V s
B. V 0 = D V s
C. V 0 = V s / D
D. V 0 = V s / ( 1 – D )
The effects of EMI can be reduced by:
A. Suppressing emissions
B. Reducing the efficiency of the coupling path
C. Reducing the susceptibility of the receptor
D. All of these
Choppers is a:
A. AC – DC converters
B. AC – AC converters
C. DC – AC converters
D. DC – DC converters
In BJT, switching losses occurs:
A. Only at turn – on
B. Only at turn – off
C. Both at turn on and off
D. None of these
As the breakdown voltage reached, the DIAC exhibits:
A. Negative resistance characteristics
B. Goes into avalanche condition
C. Voltage drop snaps back
D. All of these
DIAC are specifically designed to trigger:
A. TRIAC
B. SCR
C. GTO
D. Only (a) and (b)
In a 3 phase bridge rectifier the ripple frequency is:
A. Equal to the input frequency
B. Twice the input frequency
C. Three times the input frequency
D. Six times the input frequency
For power output higher than 15 kW, the suitable rectifier is:
A. Single phase
B. 3 phase
C. Poly phase
D. Only (b) and (c)
In a full wave rectifier, the rectification ratio is approximately equal to:
A. 61%
B. 71%
C. 81%
D. 91%
In a single phase full wave rectifier, during blocking state the pea inverse voltage of diode is:
A. V m
B. 2 V m
C. V m / 2
D. 4 V m
A single phase ac – dc converter is also known as:
A. rectifier
B. inverter
C. chopper
D. regulator
If the gate voltage of an SCR is removed, then the:
A. anode current decreases
B. anode current does not decrease at all
C. anode current increases
D. cathode current increases
Anode of an operational SCR is:
A. Always positive w.r.t cathode
B. Always negative w.r.t anode
C. Always positive w.r.t anode
D. Always negative w.r.t cathode
In a silicon controlled rectifier, the load is connected:
A. Across anode
B. In series with anode
C. Across cathode
D. In series with cathode
AC power in a load can be controlled by using:
A. Two SCR’s in parallel opposition
B. Two SCR’s in series
C. Three SCR’s in series
D. Four SCR’s in series
Number of PN junction in an SCR is:
A. Two
B. Three
C. Four
D. Five
IGBT stands for:
A. Insulated gate bipolar transistor
B. Insulated gate bidirectional transistor
C. Inductive gate bipolar transistor
D. Inductive gate bidirectional transistor
An ideal switch is:
A. Lossless
B. Carry current in any direction when it is on
C. Does not carry any current in any direction when it is off
D. All of these
A rectifier with an external low pass filter is an example of:
A. Indirect switch matrix circuits
B. Direct switch matrix circuits
C. Embedded converters
D. All of these
What is the advantage of HRC fuses over Rewirable fuses:
A. High speed operation
B. High rupturing capacity
C. No ageing effect
D. All of the above
The power demand can be estimated approximately by:
A. Load survey method
B. Mathematical method
C. Statistical method
D. Economic parameters
Unipolar modulation is generally used in:
A. AC – AC converters
B. AC – DC converters
C. DC – AC converters
D. DC – DC converters
Maximum di / dt in a SCR is:
A. Directly proportional to Vm of supply voltage
B. Inversely proportional to Vm
C. Inversely proportional to L
D. Both A and C
By which one of the following we can measure the reliability of a string:
A. String efficient
B. Reliability factor
C. Factor of safety
D. Derating factor
Anode current in an SCR consists of:
A. holes only
B. electrons only
C. either electron or holes
D. Both electron and holes
To meet high current demand we use SCRs in:
A. series connection.
B. parallel connection.
C. anti parallel connection.
D. both B and C.
Dynamic equalising circuit is useful:
A. To limit di / dt of SCR
B. To limit dV / dt of SCR
C. For voltage equalisation
D. Both B and C
SCRs are used in series to meet:
A. high current demand
B. low voltage demand
C. low current demand
D. high voltage demand
Which following is a two terminal three layer device:
A. BJT
B. Power dioed
C. MOSFET
D. None of above
ON state voltage drop across SCR lie between the range:
A. 0 – 0.5 V.
B. 0.5 – 1 V.
C. 1 – 1.5 V.
D. 1.5 – 2 V.
Which of following is not a power transistor:
A. IGBTs
B. COOLMOS
C. TRIAC
D. SITS
Which of following is normally ON device:
A. SIT
B. BJT
C. TRIAC
D. IGBT
Typical range of thyristor turn OFF time is:
A. 3 – 10 µs
B. 3 – 50 µs
C. 3 – 100 µs
D. 3 – 500 µs
Power transistor are type of:
A. B.JTs
B. MOSFETs
C. IGBTs
D. All of above
A GTO can be turned on by applying:
A. Positive gate signal
B. Positive drain signal
C. Positive source signal
D. None of these
SITH is also known as:
A. Filled controlled diode
B. Filled controlled rectifier
C. Silicon controlled rectifier
D. None of these
The typical time of rising time lies between:
A. 10 – 20 µs
B. 40 – 60 µs
C. 1 – 4 µs
D. 90 – 100 µs
Maximum power loss occurs during:
A. delay time
B. rise time
C. spread time
D. all
A power MOSFET has three terminals called:
A. Collector, emitter and gate
B. Drain, source and gate
C. Drain, source and base
D. Collector, emitter and base
Materials used in heat sink should have:
A. high thermal conductivity
B. large surface area
C. high melting point
D. All of these
A thyristor can termed as:
A. AC switch
B. DC switch
C. Both a and B
D. Square wave switch
Which of the following is used in heat sink:
A. Iron
B. Aluminium
C. Carbon
D Silver
How can we protect SCR from thermal conditions:
A. Use of snubber circuit.
B. Using heat sink.
C. Using CB and fuse.
D. Using equalizing circuit
Thyristor is nothing but a:
A. Controlled transistor
B. Controlled switch
C. Amplifier with higher gain
D. Amplifier with large current gain
Gate circuit or triggering circuit of a thyristor is:
A. lower power circuit.
B. high power circuit.
C. magnetic circuit.
D. may be low power or high power circuit
After proper turn on of thyristor:
A. gate signal is always present
B. gate signal must be removed
C. gate signal should present
D. none of the above.
What is used to protect a thyristor from high di / dt conditions:
A. Fuse.
B. Snubber circuit
C. Inductor
D. Voltage clamping device
COOLMOS device can be used in application up to power range of:
A. 1 KVA
B. 2 KVA
C. 500 VA
D. 100 KVA
Snubber circuit is used with SCR:
A. in series
B. in parallel
C. either series or parallel
D. anti parallel
Why resistor is used in Snubber circuit:
A. To minimize the loss
B. To minimize the charging current
C. To minimize the discharging current
D. All of these
What may happen high dV / dt:
A. Unwanted turn ON
B. Breakdown of J2 junction
C. Both A and B
D. Anyone of these
Thermal voltage VT can be given by:
A. Kq/T
B. KT/q
C. qT/K
D. (K2/q)(T + 1/T – 1)
IGBT combines the advantages of:
A. BJTs and SITs
B. BJTs and MOSFETs
C. SITs and MOSFETs
D. None of these
Which of the following is used in SCR to protect from high dV / dt:
A. Snubber circuit
B. Fuse
C. Equalizing circuit
D. Circuit breaker
BCT is used for:
A. High power phase control
B. High power current control
C. Low power current control
D. Low power phase control
Which of following devices has highest di/dt and dv/dt capability:
A. SIT
B. SITH
C. GTO
D. SCR
Which triggering is the most reliable:
A. forward blocking mode
B. reverse blocking mode
C. both forward and reverse blocking mode
D. forward conduction mode
Which of the following is disadvantage of fast recovery diodes:
A. Recovery is only 5 µs
B. Recovery is only 50 µs
C. Doping is carried out
D. None of these
A power semiconductor may undergo damage due to:
A. High di/dt
B. High dv/dt
C. Low di/dt
D. Low dv/dt
If the anode current is 800 A, then the amount of current required to turn off the GTO is about:
A. 20 A
B. 200 A
C. 600 A
D. 400 A
What is used to protect the SCR from over current:
A. CB and fuse.
B. Heat sink.
C. Snubber circuit.
D. Voltage clamping device
Which semiconductor device acts like a diode and two transistor:
A. UJT
B. Diac
C. Triac
D. SCR
Under over voltage condition impedance offered by the voltage clamping device is:
A. low
B. High
C. moderate
D. infinity
The latching current of GTO should be of order:
A. 100 mA
B. 500 mA
C. 1 A
D. 2 A
The maximum di/dt in a SCR is:
A. Directly proportional to supply voltage
B. Directly proportional to inductance in the circuit
C. Inversely proportional to supply voltage
D. Both A and B
Example of a voltage clamping device:
A. fast acting fuse
B. snubber circuit
C. metal oxide varistor
D. aluminium block
Switching frequency of SITH is:
A. 5 KHz
B. 10 KHz
C. 60 KHz
D. 100 KHz
Thyristor can be protected from over voltages by using:
A. voltage clamping device.
B. fuse.
C. heat sink.
D. snubber circuit.
Thyristor can be protected from over voltages by using:
A. 23 mA.
B. 40 mA.
C. 10 mA.
D. 60 mA.
The function of snubber circuit connected across the SCR is to:
A. Suppress dV / dt.
B. Increase dV / dt.
C. Decrease dV / dt.
D. Decrease di / dt.
If holding current of a thyristor is 2 mA then latching current should be:
A. 0.01 A.
B. 0.002 A.
C. 0.009 A.
D. 0.004 A.
A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty cycle is:
A. 0.32
B. 0.67
C. 0.45
D. 0.27
A single phase full bridge inverter can operated in load commutation mode in case load consist of:
A. RL.
B. RLC underdamped.
C. RLC overdamped.
D. RLC critically damped
The typical value of SCR for modern alternator is:
A. 1.5.
B. 0.5.
C. 1.0.
D. 1.2.
A Triac has three terminals viz:
A. Drain, source, gate
B. Two main terminal and a gate terminal
C. Cathode, anode, gate
D. None of the above
A thyristor is basically:
A. PNPN device
B. A combination of diac and triac
C. A set of SCRs
D. A set if SCR,diac and triac
A PNPN device having two gates is:
A. Diac
B. Triac
C. SUS
D. BCS
A silicon controlled racitifier (SCR) is a:
A. Unijunction device
B. Device with three junction
C. Device with four junction
D. None of the above
A thyristor equivalent of a thyratron tube is a:
A. Diac
B. Triac
C. Silicon controlled-rectifier SCR
D. None of above
A Triac is a:
A. 2 terminal switch
B. 2 terminal bilateral switch
C. 3 terminal bilateral switch
D. 3 terminal bidirectional switch
Which of the following quantities consists of SI unit as WATT:
A. Force
B. Charge
C. Current
D. Power
Which of the following has no units:
A. Permeability
B. Moment of a magnet
C. Magnetic susceptibility
D. Permittivity
Which quantity consists of a unit 1KWh:
A. Energy
B. Time
C. Power
D. Charge
Which quantity should be measured by the voltmeter:
A. Current
B. Voltage
C. Power
D. Speed
Internal resistance of ideal current source is:
A. zero
B. infinite
C. finite
D. 100 ohms
Capacitor does not allow the sudden change of:
A. current
B. voltage
C. power
D. None of the above
Power dissipation in ideal inductor is:
A. Maximum
B. Minimum
C. Zero
D. A finite value
Which of the following are the passive elements:
A. Resistor
B. Bulb
C. Both
D. None of these.
If 1 A current flows in a circuit, the number of electrons flowing through this circuit is:
A. 0.625 × 1019
B. 1.6 × 1019
C. 1.6 × 10-19
D. 0.625 × 10-19
The resistivity of the conductor depends on:
A. area of the conductor.
B. length of the conductor.
C. type of material.
D. none of these.
How many coulombs of charge flow through a circuit carrying a current of 10 A in 1 minute:
A. 10
B. 60
C. 600
D. 1200
The unit of resistivity is:
A. Ω.
B. Ω – metre.
C. Ω / metre.
D. Ω / m².
Magnetic flux has the unit of:
A. Newton
B. Ampere-turn
C. Weber
D. Tesla
Which of the followings is/are active element:
A. Voltage source
B. Current source
C. Both
D. None of these
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