Explore topic-wise MCQs in Electrical Engineering.

This section includes 227 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.

51.

Calculate the output voltage of the Buck converter if the supply voltage is 789 V and duty cycle value is .9.

A. 711.1 V
B. 710.1 V
C. 722.2 V
D. 713.2 V
Answer» C. 722.2 V
Discussion
52.

Calculate the output voltage of the Boost converter if the supply voltage is 156 V and duty cycle value is .4.

A. 260 V
B. 264 V
C. 261 V
D. 268 V
Answer» B. 264 V
Discussion
53.

In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally

A. Equal
B. Different
C. equal or different
D. different but sometimes equal
Answer» B. Different
Discussion
54.

A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin t. The thyristor will conduct

A. from 0 to 180
B. when v > 50 V
C. from 0 to 90
D. When v < 50 V
Answer» C. from 0 to 90
Discussion
55.

Thyristors connected in series need static and dynamic stabilizing circuits.

A. True
B. False
C. none
D. all
Answer» B. False
Discussion
56.

In a 3 phase full converter, the instantaneous output voltage can have negative part if

A. firing angle is less than 60
B. firing angle is less than 90
C. firing angle is more than 60
D. firing angle is more than 90
Answer» D. firing angle is more than 90
Discussion
57.

In a 3 phase full converter the average load current is 150 A. The average thyristor current is

A. 150 A
B. 75A
C. 50 A
D. 25 A
Answer» D. 25 A
Discussion
58.

When thyristors are connected in series and parallel, it may be necessary to have :

A. current derating
B. voltage derating
C. both current and voltage derating
D. none of the above
Answer» D. none of the above
Discussion
59.

Assertion (A): A TRIAC is a bidirectional SCR. Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» B. Both A and R correct but R is not correct explanation of A
Discussion
60.

For dynamic equalizing circuit used for series connected SCRs, the choice of C is based on:

A. Reverse recovery characteristics
B. Turn-on characteristics
C. Turn-off characteristics
D. Rise time characteristics
Answer» B. Turn-on characteristics
Discussion
61.

A combination of synchronized leading edge and trailing edge modulation has also been used to control a____________?

A. Boost single – phase power factor converter
B. A buck dc – dc converter to reduce ripple in the intermediate dc bus capacitor
C. Both A. and B.
D. None f these
Answer» D. None f these
Discussion
62.

A carrier based PWM technique in CSI is composed of____________?

A. A switching pulse generator and a shorting pulse generator
B. A shorting pulse distributor
C. A switching and shorting pulse combination
D. All of these
Answer» E.
Discussion
63.

A capacitive load in voltage source inverters generates ________________?

A. Small current spikes and can be reduced by using an inductive filter
B. Large current spikes and can be increased by using an inductive filter
C. Small current spikes and can be increased by using an inductive filter
D. Large current spikes and can be reduced by using an inductive filter
Answer» E.
Discussion
64.

60 thyrsistors are connected in series and parallel to form a 10 KV and 5.5 KA switch. Each thyristor is rated for 1.2 KV, 1 KA. The no. of parallel path are 6. The efficiency of the switch is______________________?

A. 76.3 %
B. 91.6 %
C. 83.3 %
D. 90.9 %
Answer» B. 91.6 %
Discussion
65.

4 thyristors rated 200 V in series. The operating voltage of the string is 600 V. Derating factor of the string is_____________________?

A. 0.75
B. 0.7
C. 0.2
D. 0.25
Answer» E.
Discussion
66.

As the firing of a thyristor is delayed, the output voltage of a controlled rectifier decreases.

A. True
B. False
Answer» B. False
Discussion
67.

Half bridge and full bridge inverters of one type use different commutation methods.

A. True
B. False
Answer» C.
Discussion
68.

In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time.

A. True
B. False
Answer» C.
Discussion
69.

Assertion (A): Thyristors can be used in controlled heating, excitation systems of alternators, speed control of motors and HVDCReason (R): A static var system using thyristors is very commonly used in high voltage ac systems.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» C. A is correct but R is wrong
Discussion
70.

Assertion (A): The circuit of figure thyristor will conduct for 180° during positive half cycle if it is continuously fired. Reason (R): A thyristor can conduct only when it is forward biased.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» E.
Discussion
71.

Assertion (A): A transistor has lower voltage drop during conduction as compared to thyristorReason (R): Transistors are manufactured in very high voltage and current ratings.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» D. A is wrong but R is correct
Discussion
72.

Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.Reason (R): Transistor find widespread application in power electronic circuits.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» D. A is wrong but R is correct
Discussion
73.

Assertion (A): SUS is a PUT and avalanche diode connected between gate and cathodeReason (R): SBS has two SUS inbuilt together and connected in anti-parallel

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» C. A is correct but R is wrong
Discussion
74.

Assertion (A): Typical value of thermal resistance from source to sink of an SCR is about 0.3° C/WReason (R): Heat sinks of thyristors are generally made of aluminium.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» C. A is correct but R is wrong
Discussion
75.

Assertion (A): A TRIAC is a bidirectional SCR.Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» B. Both A and R correct but R is not correct explanation of A
Discussion
76.

Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» D. A is wrong but R is correct
Discussion
77.

Assertion (A): Light triggering is very suitable for HVDC transmission.Reason (R): Light triggering has the advantage of complete electrical isolation of gate circuit.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer» B. Both A and R correct but R is not correct explanation of A
Discussion
78.

If peak value of input voltage is Vm and firing angle is a, the average output voltage for single phase half wave and single phase full wave regulators are

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
79.

In figure, thyristor Th is in off state. When thyristor is turned on, the peak thyristor current can be

A. 5 A
B. 10 A
C. 15 A
D. 20 A
Answer» D. 20 A
Discussion
80.

A capacitor C farads is charged to a voltage V. It discharges through a thyristor, a diode and an inductance L. The peak current in the circuit is

A. VCL
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
81.

In the circuit of figure, the load current when thyristor is off

A. is constant
B. increases exponentially
C. decreases exponentially
D. zero
Answer» D. zero
Discussion
82.

In the circuit of figure, the waveshape of load current when thyristor conducting is

A. constant
B. increasing exponentially
C. decreasing exponentially
D. either (b) or (c)
Answer» C. decreasing exponentially
Discussion
83.

In a step down chopper using time ratio control, the input voltage is V and duty cycle is a. The load is purely resistive having resistance R. The average and rms load currents are

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
84.

In a certain inverter circuit each thyristor carries 26.67 A for 60°, 13.33 A for 120° and zero A for 180° of the cycle. The rms current of thyristor is

A. 20 A
B. 13.33 A
C. 6.67 A
D. 3.33 A
Answer» C. 6.67 A
Discussion
85.

A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of thyristor current is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
86.

A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of load current is

A. 40 A
B. 20 A
C. 10 A
D. 5 A
Answer» C. 10 A
Discussion
87.

In a 3 phase bridge inverter with 120° mode of operation the. number of thyristors conducting at one time are

A. 1
B. 2
C. 3
D. 4
Answer» C. 3
Discussion
88.

In a 3 phase bridge inverter with 180° mode of operation the numbers of thyristors conducting at one time are

A. 1
B. 2
C. 3
D. 4
Answer» D. 4
Discussion
89.

In a full bridge inverter fed by a battery of voltage V, the rms value of fundamental component of output voltage is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
90.

In a half bridge inverter circuit fed by a battery of voltage V, the rms value of fundamental component of output voltage is

A. 2 V
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
91.

If 0.5 T is the time period of oscillations and Toff is the time between turn off of one thyristor and turn on of second thyristor, the frequency of output f of a series inverter is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
92.

In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage

A. will have positive part only
B. will have both positive and negative parts
C. may have both positive and negative parts
D. will have negative part if load is inductive
Answer» B. will have both positive and negative parts
Discussion
93.

In a 3 phase full converter, the instantaneous output voltage can have negative part if

A. firing angle is less than 60°
B. firing angle is less than 90°
C. firing angle is more than 60°
D. firing angle is more than 90°
Answer» D. firing angle is more than 90°
Discussion
94.

A 3 phase fully controlled bridge converter is fed by a 3 phase system having phase voltage v = Vm sin ωt. The firing angle is a. The dc output voltage is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
95.

Two single phase semi-converters are connected in series to form a series converter. The input is v = Vm sin ωt and a1, a2 are the firing angles. If a1 = 0, the dc output voltage is

A. (1 + cos a2)
B. (2 + cos a2)
C. (3 + cos a2)
D. (4 + cos a2)
Answer» D. (4 + cos a2)
Discussion
96.

Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin ωt and a1 = a2 are the firing angles of the two converters. If a1 = a2 = 0, the dc output voltage is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» D. [D].
Discussion
97.

For a single phase half wave converter feeding a resistive load, the firing angle a. The waveshape in below figure is for

A. output voltage
B. input voltage
C. voltage drop across thyristor
D. none of the above
Answer» E.
Discussion
98.

A fully controlled bridge converter is feeding an RLE load. For some circuit conditions firing angle is 47°. If connections of battery are reversed, the firing angle is likely to be

A. 47°
B. less than 47°
C. more than 47°
D. either more or less than 47°
Answer» D. either more or less than 47°
Discussion
99.

A fully controlled bridge converter is feeding an RLE load. The load current is I0. The input voltage is Vm sin ωt. The KVL equation to find firing angle a is

A. cos a = E + I0R
B. cos a = E + I0R
C. cos a = E - I0R
D. cos a = E - I0R
Answer» B. cos a = E + I0R
Discussion
100.

In the below figure the rms voltage across each half of secondary is 200 V. The peak inverse voltage across each of thyristor is

A. 200 V
B. 2(200) V
C. 2(400) V
D. 800 V
Answer» D. 800 V
Discussion