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.

101.

In the below figure, the average value of load current is 15 A. The load is highly inductive. The peak value of thyristor current is

A. 15 A
B. 152 A
C. [C].
D. 30 A
Answer» B. 152 A
Discussion
102.

In the below figure, the load is highly inductive. The firing angle is a for each of the thyristors. The periods of conduction of Th1 and Th2 respectively are

A. 0 to p and p to 2p
B. a to p and p + a to 2p
C. a to p + a and p + p to 2p + a
D. a to p - a and p + a to 2p - a
Answer» D. a to p - a and p + a to 2p - a
Discussion
103.

In a single phase full wave converter (M-2 connection) feeding on R-L load the input voltage is v = Vm sin ωt. The expression for rms output voltage is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
104.

In a single phase full wave converter (M-2 connection) feeding on R - L load, the input voltage is v = Vm sin ωt. The expression for dc output voltage is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» D. [D].
Discussion
105.

In a single phase full bridge converter (B - 2 connection), the input voltage is v = Vm sin ωt. The output dc voltage for resistive load

A. [A].
B. [B].
C. [C].
D. [D].
Answer» D. [D].
Discussion
106.

In a single phase full wave converter (M - 2 connection), the rms transformer voltage is 300 V across each half of secondary. The PIV for each thyristor is

A. 300 V
B. [B].
C. 6002 V
D. [D].
Answer» D. [D].
Discussion
107.

A single phase half wave controlled rectifier circuit is feeding on RL load. The circuit has a freewheeling diode. The input voltage is v = Vm sin ωt. If I0 is the load current during the conduction of freewheeling diode, the KVL equation during the conduction of free wheeling diode is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
108.

A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30°, the dc output voltage will be about

A. 127 V
B. 120 V
C. 110 V
D. 100 V
Answer» C. 110 V
Discussion
109.

A single phase half wave rectifier is feeding a resistive load. Input voltage v = Vm sin ωt. The output dc voltage is Vdc and output rms voltage is Vrms . If firing angle is 180°, Vdc and Vrms respectively are

A. 0 and 0
B. [B].
C. 0 and - Vm
D. [D].
Answer» B. [B].
Discussion
110.

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 ωt. 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
111.

A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is

A. zero
B. about 1 V
C. same as input voltage
D. twice the input voltage
Answer» D. twice the input voltage
Discussion
112.

A single phase half wave converter is feeding-a resistor load. The input voltage is v = Vm sin ωt. If firing angle is zero, the output dc voltage Vdc and output rms voltage Vrms respectively

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
113.

A rectifier is fed by a transformer. The rms voltage and current at secondary of transformer are Vs and Is. Output dc power is Vdc Idc and output ac power is (Vrms ) (Irms), Transformer utilisation factor TUF is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
114.

The circuit in figure is for

A. resonant commutation
B. self commutation
C. load commutation
D. auxiliary commutation
Answer» C. load commutation
Discussion
115.

An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be

A. 50 A
B. 25 A
C. less than 50 A but more than 25 A
D. less than 25 A
Answer» D. less than 25 A
Discussion
116.

An SCR is triggered at 80° in the positive half cycle, only. The rms anode current is 25 A. If the firing angle is changed to 160°, the rms current is likely to be

A. 25 A
B. 12.5 A
C. less than 25 A
D. less than 12.5 A
Answer» E.
Discussion
117.

A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, the turn on time will be

A. 6 μs
B. less than 6μs
C. more than 6 μs
D. either 6 μs or less
Answer» D. either 6 μs or less
Discussion
118.

A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is

A. 20 W
B. 50 W
C. 92 W
D. 128 W
Answer» C. 92 W
Discussion
119.

An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about

A. 2 μs
B. 5 μs
C. 20 μs
D. 50 μs
Answer» C. 20 μs
Discussion
120.

A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20°C. If thermal resistance is 1.6° C/W, the junction temperature is

A. 114°C
B. 164°C
C. 94° C
D. 84° C
Answer» E.
Discussion
121.

A thyristor has maximum allowable junction temperature of 110° C and the ambient temperature is 40°C, If the maximum internal power dissipation is 50 W, the thermal resistance is

A. 2° C/W
B. 1.4° C/W
C. 0.7°C/W
D. 2.2° C/W
Answer» C. 0.7°C/W
Discussion
122.

The turn on characteristics of a power transistor can be assumed to be linear, as shown in the below figure . During turn on time T, voltage reduces linearly from V to 0 and current rises linearly from 0 to I. The energy loss during time T is

A. VIT
B. [B].
C. [C].
D. [D].
Answer» E.
Discussion
123.

Which of the following is correct for a BJT?

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
124.

For a BJT a = 0.98, then β =

A. 0.02
B. 0.5
C. 4.9
D. 49
Answer» E.
Discussion
125.

The symbol in figure is for

A. SUS
B. SBS
C. Shockley diode
D. UJT
Answer» D. UJT
Discussion
126.

A dc series motor is coupled to a load whose torque is proportional to speed. It is fed by a single phase ac supply through a full converter. When speed is 500 rpm, firing angle is 45°. It is desired to raise the speed. It will be necessary to

A. decrease the firing angle
B. increase the firing angle
C. either decrease or increase the firing angle depending on the required speed
D. decrease the load torque
Answer» B. increase the firing angle
Discussion
127.

A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be

A. about 300 rpm
B. about 150 rpm
C. about 75 rpm
D. about zero
Answer» B. about 150 rpm
Discussion
128.

A dc separately excited motor has constant field current. The armature is fed from a single phase supply through a full converter. When a = 0, speed is 500 rpm. If a = 45°, the speed is likely to be

A. about 350 rpm
B. about 250 rpm
C. about 175 rpm
D. about 125 rpm
Answer» E.
Discussion
129.

A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is

A. 25% of maximum
B. 50% of maximum
C. 75% of maximum
D. none of the above
Answer» C. 75% of maximum
Discussion
130.

In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be

A. 400 V
B. about 100 V
C. about 20 V
D. zero
Answer» E.
Discussion
131.

In a 3 phase full wave regulator feeding a star connected resistance load, firing angle is 75°. Then the number of thyristors conducting at one time is

A. 1
B. 2
C. 3
D. 4
Answer» C. 3
Discussion
132.

A single phase full wave regulator feeds a resistive load. The firing angle of thyristors is 90°. The input power factor is

A. 1
B. 0.707 lagging
C. 0.5 lagging
D. 0.2 lagging
Answer» C. 0.5 lagging
Discussion
133.

In a single phase full wave regulator, the rms current in each thyristors is Ir The run load current is equal to

A. 2Ir
B. 2 Ir
C. Ir
D. [D].
Answer» C. Ir
Discussion
134.

In a single phase full wave regulator feeding an R-L load, the power factor angle of load is θ. The range of control of firing angle a is

A. 0 ≤ a ≤ p
B. θ ≤ a ≤ p
C. 0 ≤ a ≤ (p - θ)
D. θ ≤ a ≤ (p + θ)
Answer» C. 0 ≤ a ≤ (p - θ)
Discussion
135.

In auxiliary commutated chopper fed by voltage V and having L and C commutating elements, the peak value of capacitor current is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» D. [D].
Discussion
136.

A dc chopper is feeding an RLE load. The maximum steady state ripple is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
137.

The duty cycle of a step down chopper is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
138.

If Ar and Ac are the amplitudes of reference and control signals, the modulation index M is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
139.

All other parameters remaining the same, a 3 phase bridge inverter with 180° mode of operation

A. has the same peak thyristor current as in 120° mode of operation
B. has higher peak thyristor current than in 120° mode of operation
C. has lower peak thyristor current than in 120° mode of operation
D. any of the above
Answer» C. has lower peak thyristor current than in 120° mode of operation
Discussion
140.

In an n stage high frequency series inverter having a time period T, each stage is active for a time interval of

A. T
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
141.

In a series inverter supplying a load resistance R, the commutating elements L and C should be such that

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
142.

A single phase converter is fed by a source having an inductance L. If load current is I0, the decrease in output voltage due to overlap is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» D. [D].
Discussion
143.

An n pulse rectifier is fed by a source having an inductance L. If load current is I0, the voltage drop due to overlap is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
144.

A single phase fully controlled bridge converter is feeding an RLE load. Input voltage is Vm sin ωt and firing angle is a. If average current is I0, then

A. cos a = RI0 + E
B. cos a = RE0 + E
C. cos a = E0 - RI0
D. cos a = E - RI0
Answer» B. cos a = RE0 + E
Discussion
145.

A single phase fully controlled bridge converter is fed by a voltage Vm sin ωt. The average and rms values of output voltage are

A. [A].
B. [B].
C. cos a and Vm
D. cos a and 2 Vm
Answer» B. [B].
Discussion
146.

In a single phase full wave controlled rectifier using centre tap transformer, the voltage across each half of secondary is Vm sin ωt. The peak inverse voltage is

A. 2 Vm
B. Vm
C. 0.5 Vm
D. 0.25 Vm
Answer» B. Vm
Discussion
147.

The factor η for a UJT is about

A. 0.1
B. 0.2
C. 0.6
D. 0.9
Answer» D. 0.9
Discussion
148.

A triac has ___________ semiconductor layers.

A. wo
B. hree
C. our
D. ive
Answer» D. ive
Discussion
149.

A diac is simply ___________.

A. single junction device
B. three junction device
C. triac without gate terminal
D. one of the above
Answer» D. one of the above
Discussion
150.

A diac is ___________ switch

A. n c.
B. d.c.
C. mechanical
D. one of the above
Answer» B. d.c.
Discussion