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Electronics MCQs are given here which are very helpful to the candidates who have done their degrees in Electronics Engineering or Electrical Engineering can become an officers in Pak Army, Pak Navy and PAF.

Electronics questions MCQs are very important for initial tests of Pak Army lady Cadet Course (LCC), Direct Short Service commission, PAF Engineering, and Navy Commissioned Officers.

All past papers of Electronics MCQs PDF are also given to get 100% success in initial tests of Pak Forces. For online practice tests click here.

Which of the given device is the fastest switching device

1. MOSFET
2. Triode
3. BJT
4. JEFT

A snubber circuit is used to

1. Limit the rate of rising in voltage across BJT
2. Limit the rate of rising in voltage across SCR
3. Limit the rate of rising in current across TRIAC
4. Limit the rate of rising in current across BJT

If the maximum value of applied voltage for a full-wave center ap (M-2) rectifier is 30 V, find the magnitude of ripple voltage

1. 88
2. 84.52
3. 87.62
4. 89.59

In the forward blocking mode of a silicon controlled rectifier, the SCR is

1. In on state
2. In natural state
3. Forward biased state
4. In off state

## Digital Electronics MCQs

A silicon controlled rectifier is turned on if the anode current is greater than

1. Trigger current
2. Anode current
3. Cathode current
4. Holding current

The anode current passing through a conducting silicon-controlled rectifier is 20 A. If its gate current is made half, what will be the anode current?

1. 10 A
2. 20 A
3. 5 A
4. 30 A

A silicon controlled rectifier is turned off mode when its turn off time is

1. Greater than the circuit turn off time
2. Less than the circuit turn off time
3. Equal to the circuit turn off time
4. None of these

A 1 – ∅ full-wave rectifier is made by using thyristors. If the peak value of the sinusoidal input voltage is Vm and the value of the delay angle is ?/4 radian, find the average value of output voltage

1. 25 V
2. M
3. 0.45 VM
4. 0.65 VM
5. 0.85 VM

The TRIAC is the same as

1. Two SCR connected in parallel
2. Two SCR connected in antiparallel
3. One SCR and one thyristor connected in parallel
4. Two SCR connected in series

A half-wave rectifier circuit using an ideal diode has an input voltage of 10 sin ?t V; find the average and RMS value of output voltage?

1. 18 V, 5V
2. 3.68 V, 8V
3. 4.18 V, 5V
4. 4.68 V, 8V

A solar cell of 450 V supplies power to an ac source of 440 V, 50 Hz through a 3 phase fully controlled bridge converter. An inductance with a value of 10 A is connected to the dc circuit to maintain the dc current. If the resistance of the solar cell is 1 Ω, each thyristor will be reverse biased for a period of

1. 1480
2. 1380
3. 1280
4. 1180

## Electronics Interview Questions

A 1 – ∅ full wave rectifier is designed using thyristors. It the peak value of the sinusoidal input voltage Vm and the delay angle isradian, find the average value of output voltage?

1. 35 Vmax
2. 0.45 Vmax
3. 0.55 Vmax
4. 0.65 Vmax

Which of the given device is the most suitable power device for a higher frequency (above 100 kHz) switching application

1. SCR
2. Power MOSFET
3. GTO
4. BJT

Which of the given device is a modern semiconductor device that combines the characteristics of MOSFET and BJT?

1. SCR
2. Schottky diode
3. Microwave transistor
4. IGBT

The thyristor is equivalent to a thyratron tube is

1. BJT
2. SCR
3. TRIAC
4. GTO

A single-phase controlled, a full-bridge converter is supplying a highly inductive DC load. The conductor is fed from a 220 V, 50Hz, ac source. Find the fundamental frequency in Hz of the voltage ripple on the dc side

1. 300 Hz
2. 220 Hz
3. 100 Hz
4. 50 Hz

A single-phase fully controlled thyristor bridge ac dc converter is operating at a firing angle is 300 and overlap angle is 200 constant dc output current of 10 A. find the fundamental power factor at input ac mains?

1. 968
2. 0.766
3. 0.163
4. 0.586

Find the average output of a semiconverter connected to a 220 V, 50 Hz power supply, and firing angle is

1. 52
2. 248.05
3. 148.55
4. 198.49

A freewheeling diode is phase-controlled rectifiers.

1. Stops rectifier operations
2. Improves line power factor
3. Is the reason for additional harmonics
4. Is the reason for the sudden breakdown

## Basic Electronics Questions

In a three-phase bridge rectifier, the maximum conduction of each thyristor is

1. 1200
2. 900
3. 300
4. 600

In a 3-∅ controlled bridge rectifier, the frequency of ripple in the output voltage depends on

1. Power factor
2. Supply frequency
3. Voltage source
4. Firing angle

A three-phase full converter is supplying a purely resistive load at 220 V dc for 00 firing angle, find the output voltage for 900 firing angle

1. 30 V
2. 0 V
3. 90 V
4. 120 V

What is the name of a converter which can work on both in 3-pulse and 6 pulse modes?

1. Three-phase full-wave converter
2. Three-phase half wave converter
3. Three-phase semi converter
4. Single-phase semi converter

A three phase full controlled converter can operate as a

1. Converter for α = 0 to 1200
2. Converter for α = 0 to 900
3. Converter for α = 0 to 1800
4. Converter for α = 0 to 600

A 3 phase, 6 pulse SCR converter is connected to a voltage source of 220 V, 50 Hz, AC mains, and controlling a dc drive with terminal voltage 210 V and rated current value is 90 A. If the commutation angle µ = 15and firing angle α= 60,0, find the rating of shunt compensator and power factor.

1. 1
2. 0.5
3. 2
4. 1.5

Which of the given regulator provide output voltage polarity reversal without the involvement of a transformer.

1. Linear voltage regulator
2. Shunt voltage regulator
3. Buck-Boost regulator
4. Series voltage regulator

A chopper converts

1. AC to DC
2. AC to AC
3. DC to AC
4. DC to DC

A chopper circuit works on TRC control mode at a frequency of 4 kHz of a 220 V dc supply. For 180 V output voltage, find the conduction and blocking periods of a thyristor in each cycle.

1. 209 ms, 0.234 ms
2. 0.404 ms, 0.055 ms
3. 0.204 ms, 0.045 ms
4. 0.704 ms, 0.897 ms

A four-quadrant chopper can not be operated as

1. Thyristor
2. Cycloconverter
4. Inverter

If a step-up chopper has source voltage V and duty cycle α, find the chopper’s output voltage.

How many switches are used to build a three-phase to three-phase cycloconverter?

1. 10
2. 14
3. 18
4. 24

A three-phase to three-phase cyclo converter requires

1. 24 SCRs for 6 pulse device
2. 36 SCRs for 6 pulse device
3. 48 SCRs for 3 pulse device
4. 24 SCRs for 3 pulse device

A three-phase cycloconverter is used to find the variable frequency single-phase ac output. If the single-phase ac load is 240 V, 50 A at a power factor of 0.8 lagging, find the RMS value of input voltage per phase

1. 220 V
2. 240 V
3. 290 V
4. 20 V

A single-phase, half-bridge inverter has an input voltage of 60 VDC. If the inverter is feeding a load of 3.6 ohms, find the RMS output voltage at a fundamental frequency

1. 188 V
2. 168 V
3. 158 V
4. 178 V

## Basic Electronics Questions and Answers

PWM switching is used in voltage source inverters for the purpose of

1. Controlling output current
2. Controlling input voltage
3. Controlling input power
4. Controlling output harmonics and output voltage.

A single-phase full-bridge voltage source inverter (VSI) is fed from a 240 V dc source. If a pulse of 600 duration is used to trigger the devices in each half-cycle, find the RMS value of the fundamental component of the output voltage.

1. 128 v
2. 148 V
3. 108 V
4. 168 V

An electric motor, developing a starting torque of 18 Nm, starts with a load toque of 9 Nm on its shaft. If the acceleration at the initial point is 3 rad/sec2, find the moment of inertia of the system(Ignore friction)

1. 3 Kg – m2
2. 9 Kg – m2
3. 27 Kg – m2
4. 81 Kg – m2

If a 3 phase semi converter is feeding by a separately excited dc motor at constant field current, the motor can operate in the given condition.

1. Speed positive and toque negative
2. Speend positive and toque positive
3. Speed negative and toque positive
4. Speed negative and toque negative

A 240 V, 1200 rpm. 30 A separately excited dc motor has an armature resistance of 3 ohms. A step-down chopper controls the dc motor with a frequency of 1 kHz. The input dc voltage given to the chopper is 280 V. If the duty cycle of the chopper for the motor to operate at a speed of 700 rpm, find the rated toque

1. 233
2. 0.338
3. 0.633
4. 0.951

A single-phase half-controlled rectifier is driving a separately excited dc motor. The back emf constant of the motor is 0.30 V/rpm. The armature current’s value is 8 A without any ripple, and the armature resistance is 3 ohm. The converter is working from a 240 V power supply of a single phase ac source with a firing angle of 600. Find the speed of the dc motor under this condition

1. 6 rpm
2. 168. 7 rpm
3. 190. 2 rpm
4. 240. 8 rpm

The armature current of a dc motor fed from a thyristor power converter consists of ripples. The ripple in the armature affects

1. Commutation of the motor
2. Speed of the motor
3. Toque of the motor
4. The efficiency of the motor

## Electronics Questions and Answers PDF

A motor armature is supplied through a phase control silicon controlled rectifiers receives a smoother voltage shape at

1. Lower motor speed
2. Constant motor speed
3. Higher motor speed
4. None of these

The torque produced by a single-phase induction motor fed by an ac voltage controller for speed control due to

1. A fundamental component of harmonics as well as current
2. A fundamental component of harmonics only
3. A fundamental component of current only
4. Fundamental component and even harmonics

A resistance of 4 ohms is connected in the rotor circuit, and a resistance of 8 ohms is additionally connected during OFF periods of a chopper. The OFF period of the chopper is 6 ms. Find the average resistance in the rotor circuit for the chopper frequency off 200 Hz.

1. 6 ohm
2. 15.5 ohm
3. 25.9 ohm
4. 1.8 ohm

When a self-controlled synchronous motor fed from a variable frequency inverter

1. The speed of the stator decides stator speed
2. Stability problems occur
3. The frequency of the stator decides the rotor speed
4. The frequency of the rotor decides the rotor speed

A 3-∅ fully controlled thyristor bridge converter is used as a line commutated inverter to feed 60 kW With the power 450 V dc to a three-phase, 430 V (line), 50 Hz ac mains. If the dc-link current is constant, find the RMS current of the thyristor.

1. 68 A
2. 76.98 A
3. 66.08 A
4. 16.88 A

A cycloconverter fed induction motor drive is widely used for which one of the following?

1. Compressor drive
2. Machine tool drive
3. Papermill drive
4. Cement mill drive

Which of the given configurations is used for both regenerative and motoring breaking?

## Basic Electronics MCQs with Answers PDF

A dc chopper is used in the regenerative braking mode of a dc series motor. The dc supply is 400 V, and the duty cycle is 60%. The average value of armature current is 80 A. If it is considered as continuous and ripply free, find the value of power feedback to the supply?

1. 28200 W
2. 19200 W
3. 21240 W
4. 19220 W

Power diode is

1. Two terminal semiconductor device
2. Three terminal semiconductor device
3. Four terminal semiconductor device
4. None of these

The V-I characteristics of diode lie in the

3. The third and second quadrant
4. The first and third quadrant

Find a triple frequency of a six-phase half-wave rectifier for 220 V 50 Hz input

1. 150 Hz
2. 300 Hz
3. 50 Hz
4. 600 Hz

## Basic Electronics MCQs with Answers

If a firing angle α of a single phase fully controlled rectifier feeding a constant DC current into the load is 600, Find the displacement factor of the rectifier

1. 0
2. 0.5
3. 1
4. 1.5

A forward-biased PN junction acts as a/an

1. Thyristor
2. Closed switch
3. Amplifier
4. Chopper

For a specific transistor, if the value of beta is equal to 400 and the Base current is 8mA, Find the value of Emitter current?

1. 308
2. 3.208 A
3. 7.808 A
4. 9.276 A

The two-transistor model of an SCR obtained by

1. Bisecting the SCRs diagonally
2. Bisecting the SCRs top and bottom two layers
3. Bisecting the SCRs only bottom two layers
4. Bisecting of SCRs horizontally