Power Electronics — Part 1 MCQs with Explanations

A Unijunction Transistor (UJT) has one pn junction. The UJT consists of a single pn junction between its emitter and the base regions. This single pn junction is used for the UJT's unique characteristics, including its ability to act as a trigger device in various electronic circuits. Options A and C are incorrect as UJTs do not have two or three pn junctions; the correct number is one.

A sawtooth generator is the correct answer to “The UJT may be used as ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Two is the correct answer to “A diac has ___________ pn junctions”. This question is standard in competitive examination syllabi for Power Electronics.

Two is the correct answer to “A diac has ___________ terminals.”. This question is standard in competitive examination syllabi for Power Electronics.

Bidirectional is the correct answer to “A triac is a ___________ switch”. This question is standard in competitive examination syllabi for Power Electronics.

Breakover voltage is the correct answer to “The normal way to turn on a diac is by ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Bilateral conduction is the correct answer to “Which of the following is not a characteristic of UJT”. This question is standard in competitive examination syllabi for Power Electronics.

Both positive and negative is the correct answer to “A triac can pass a portion of ___________ half-cycle through the load.”. This question is standard in competitive examination syllabi for Power Electronics.

Negative resistance is the correct answer to “Between the peak point and the valley point of UJT emitter characteristics we have ___________ region”. This question is standard in competitive examination syllabi for Power Electronics.

Negative resistance is the correct answer to “After peak point, the UJT operates in the ___________ region.”. This question is standard in competitive examination syllabi for Power Electronics.

More than is the correct answer to “To turn on UJT, the forward bias on the emitter diode should be ___________ the peak point voltage.”. This question is standard in competitive examination syllabi for Power Electronics.

Double-base is the correct answer to “A UJT is sometimes called ___________ diode.”. This question is standard in competitive examination syllabi for Power Electronics.

A breakover voltage is the correct answer to “A diac is turned on by ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

UJT is the correct answer to “The device that exhibits negative resistance region is ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

High is the correct answer to “When the emitter terminal of a UJT is open, the resistance between the base terminal is generally ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Essentially remains the same is the correct answer to “When the temperature increases, the intrinsic stand off ratio ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Heavily is the correct answer to “In a UJT, the p-type emitter is ___________ doped”. This question is standard in competitive examination syllabi for Power Electronics.

Diac is the correct answer to “The device that does not have the gate terminal is ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

SCR is the correct answer to “The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ___________ in its first quadrant”. This question is standard in competitive examination syllabi for Power Electronics.

Two main terminal and a gate terminal is the correct answer to “A Triac has three terminals viz ___________”. This question is standard in competitive examination syllabi for Power Electronics.

Increases is the correct answer to “When the temperature increases, the inter-base resistance (RBB) of a UJT ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

50 Hz frequency is the correct answer to “Power electronics essentially deals with control of a.c. power at ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

An a.c. is the correct answer to “A DIAC is ___________ switch.”. This question is standard in competitive examination syllabi for Power Electronics.

A triac without gate terminal is the correct answer to “A diac is simply ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Four is the correct answer to “A triac has ___________ semiconductor layers.”. This question is standard in competitive examination syllabi for Power Electronics.

Three is the correct answer to “A diac has ___________ semiconductor layers”. This question is standard in competitive examination syllabi for Power Electronics.

Is decreased is the correct answer to “When a UJT is turned ON, the resistance between emitter terminal and lower base terminal ___________”. This question is standard in competitive examination syllabi for Power Electronics.

Like a bidirectional SCR is the correct answer to “The triac is ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

In inverse-parallel is the correct answer to “A triac is equivalent to two SCRs ___________.”. This question is standard in competitive examination syllabi for Power Electronics.

Lower core loss is the correct answer to “SMPS normally use Ferrite core transformers in place of Iron core because of”. This question is standard in competitive examination syllabi for Power Electronics.

FET is the correct answer to “Which of the following devices does not have negative resistance characteristics”. This question is standard in competitive examination syllabi for Power Electronics.

UPS is the correct answer to “Inverters find applications in”. This question is standard in competitive examination syllabi for Power Electronics.

Depends both on the type of load and firing angle delay is the correct answer to “In controlled rectifiers, the nature of load current is continuous or discontinuous”. This question is standard in competitive examination syllabi for Power Electronics.

Forward blocking state is the correct answer to “The operating state that distinguishes a silicon controlled rectifier (SCR) from a diode is”. This question is standard in competitive examination syllabi for Power Electronics.

94.4 V is the correct answer to “For a type A chopper, DC source voltage is 240 V. Calculate the average output voltage is the duty cycle is 0.4. Take a voltage drop of 4 V across the chopper when it is on.”. This question is standard in competitive examination syllabi for Power Electronics.

Holding current is the correct answer to “In a thyristor, the minimum current required to maintain the device in the 'ON' state is called”. This question is standard in competitive examination syllabi for Power Electronics.

$$\frac{\pi }{2} < \alpha < \pi $$ is the correct answer to “For a single phase fully controlled converter bridge operating with continuous load current, the converter will operate in inverting mode for triggering angle, $$\alpha $$, such that:”. This question is standard in competitive examination syllabi for Power Electronics.

Heavily is the correct answer to “An UJT, the p-type emitter is . . . . . . . . doped”. This question is standard in competitive examination syllabi for Power Electronics.

$$\frac{{220}}{{\sqrt 2 }}{\text{V}}$$ is the correct answer to “A single-phase full-wave AC phase controller feeds power to a resistive load of 100 Ω from a 220 V, 50 Hz supply. What will be the rms output voltage at delay angles $${\alpha _1} = {\alpha _2} = \alpha = \frac{\pi }{2}$$ of both transistors”. This question is standard in competitive examination syllabi for Power Electronics.

2 and 4 is the correct answer to “Consider the following statements: A four-layer PNPN device having two gate leads can turned on by applying a 1. positive current pulse to the cathode gate 2. positive current pulse to the anode gate 3. negative current pulse to the anode gate 4. negative current pulse to the cathode gate Which of these statements is/are correct”. This question is standard in competitive examination syllabi for Power Electronics.