Multiple Choice Questions Topic Outline
- MCQs in Industrial Electronics
- MCQs in Electronic Control System
- MCQs in Industrial Solid State Services
- MCQs in Welding Systems
- MCQs in Thyristors
- MCQs in High Frequency Heating
- MCQs in Feedback Systems / Servomechanism
- MCQs in Transducers
- MCQs in Motor Speed Control Systems
- MCQs in Robotic Principles
- MCQs in Bioelectrical Principles
- MCQs in Instrumentation and Control
The Series
Following is the list of multiple choice questions in this brand new series:
Continue Practice Exam Test Questions Part V of the MCQs Series
Choose the letter of the best answer in each questions.
201. For an SCR, dv/dt protection is achieved through the use of:</>
- A. RL in series with SCR
- B. RC across SCR
- C. L in series with SCR
- D. RC in series with SCR
202. A technique use to turn off a thyristor using an external circuit which causes the anode to become negatively biased.
- A. force commutation
- B. reverse triggering
- C. negative feedback
- D. doping
203. The turn-off time of thyristor is 30 m sec at 50°C. Its turn-off time at 100° is
- A. same
- B. 15 m sec
- C. 60 m sec
- D. 100 m sec
204. The peak and valley currents of the PUT are typically _____ those of a similarly rated UJT.
- A. lower than
- B. the same as
- C. higher than
- D. None of the above
205. What is a solid state equivalent of a gas filled triode?
- A. Triac
- B. Thyristor
- C. SCR
- D. SCS
206. The method(s) for turning off an SCR is (are) categorized as _____.
- A. current interruption
- B. forced commutation
- C. both current interruption and forced commutation
- D. None of the above
207. In a certain UJT rB1 is 2.5 kΩ and rB2 = 4 kΩ. What is the intrinsic standoff ratio?
- A. 0.61538
- B. 0.38461
- C. 2.6
- D. 0.8125
208. When SCR starts conducting, then _____ losses all control.
- A. gate
- B. anode
- C. cathode
- D. anode supply
209. You have the schematic diagram of several types of circuits. Which of these circuits most likely uses a triac?
- A. an oscillator
- B. an ac motor control
- C. a programmable oscillator
- D. an amplifier
210. Determine RB1 for a silicon PUT if it is determined that h = 0.84, VP = 11.2 V, and RB2 = 5 kΩ.
- A. 12.65 kΩ
- B. 16.25 kΩ
- C. 20.00 kΩ
- D. 26.25 kΩ
211. Which of the following devices does not have a cathode terminal?
- A. SCR
- B. SCS
- C. TRIAC
- D. Shockley diode
212. The UJT operates in what region after peak point?
- A. Cut off
- B. Negative resistance
- C. Saturation
- D. Positive resistance
213. What is basically a two-terminal parallel-inverse combination of semiconductor layers that permits triggering in either direction?
- A. DIAC
- B. TRIAC
- C. QUADRAC
- D. Shockley Diode
214. Which device does not have a gate terminal?
- A. Triac
- B. SCR
- C. FET
- D. Diac
215. The four-layer devices with a control mechanism are commonly referred to as _____.
- A. thyristors
- B. transistors
- C. diodes
- D. None of the above
216. What is that voltage above when the SCR enters the conduction region?
- A. Reverse breakover voltage
- B. Forward breakover voltage
- C. Holding voltage
- D. Trigger voltage
217. It is a three-terminal silicon diode with the ability to control a large ac power with a small signal.
- A. TRIAC
- B. SCR
- C. UJT
- D. SCS
218. The smallest amount of current that the cathode-anode can have, and still sustain conduction of an SCR is called the:
- A. maximum forward current
- B. maximum forward gate current
- C. holding current
- D. reverse gate leakage current
219. It is the minimum additional current that can make up for any missing input (gate) current in order to keep the device ON.
- A. leakage current
- B. ac current
- C. holding current
- D. switching current
220. The PUT (programmable unijunction transistor) is actually a type of:
- A. UJT thyristor
- B. FET device
- C. TRIAC
- D. SCR
221. What is the typical value of the interbase resistance of UJTs?
- A. 20 KΩ
- B. Between 4 to 4 KΩ
- C. 4 KΩ
- D. Between 4 to 10 KΩ
222. Which of the following is a four-layer diode with an anode gate and a cathode gate?
- A. SCS
- B. SCR
- C. SBS
- D. SUS
223. SCR is a rectifier constructed of silicon material. Silicon is chosen because
- A. it is the most abundant material
- B. of its strength and ruggedness
- C. it is much cheaper than any other material
- D. of its high temperature and power capabilities
224. When the temperature increases, the intrinsic standoff ratio
- A. increases
- B. decreases
- C. essentially constant
- D. becomes zero
225. SCRs have been designed to control powers as high as _____, with individual ratings as high as _____ at _____.
- A. 1800 MW, 10 A, 2000 V
- B. 1800 MW, 2000 A, 10 V
- C. 10 MW, 2000 A, 1800 V
- D. 2000 MW, 10 A, 1800 V
226. An SCR is a member of what family?
- A. Thyrector
- B. Thyratron
- C. Thyristor
- D. Transistor
227. Which of the following can change the angle of conduction in SCR?
- A. Changing anode voltage
- B. Changing gate voltage
- C. Reverse biasing the gate
- D. Changing cathode voltage
228. What is the frequency range of application of SCRs?
- A. About 10 kHz
- B. About 50 kHz
- C. About 250 kHz
- D. About 1 mHz
229. The minimum operating voltage of the UJT is typically _____ that of a similarly rated PUT.
- A. lower than
- B. the same as
- C. higher than
- D. None of the above
230. A UJT is sometimes called a ____ diode.
- A. double-based
- B. single-based
- C. a rectifier
- D. a switching diode
231. It is like a low current SCR with two gate terminals.
- A. UJT
- B. PUT
- C. SCR
- D. SCS
232. What is the typical value of the reverse resistance of SCRs?
- A. 1 Ω to 10 Ω
- B. 100 Ω to 1 kΩ
- C. 1 kΩ to 50 kΩ
- D. 100 kΩ or more
233. Which of the following is the normal way to turn on a diac?
- A. By breakover voltage
- B. By gate voltage
- C. By gate current
- D. By anode current
234. In a SCR circuit, the angle of conduction can be changed by changing
- A. anode voltage
- B. anode current
- C. forward current rating
- D. gate current
235. 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
236. An SCR is made of what material?
- A. Silicon
- B. Carbon
- C. Germanium
- D. Gallium-arsenide
237. The SCR can exercise control over _____ of ac supply.
- A. positive or negative half-cycle
- B. both positive and negative half-cycles
- C. only positive half-cycle
- D. only negative half-cycle
238. Which of the following conditions is necessary for triggering system for thyristors?
- A. It should be synchronized with the main supply
- B. It must use separate power supply
- C. It should provide a train of pulses
- D. None of these
239. A normally operated SCR has an anode which is _____ with respect to cathode.
- A. negative
- B. positive
- C. at zero potential
- D. at infinite potential
240. Which of the following devices has (have) four layers of semiconductor materials?
- A. Silicon-controlled switch (SCS)
- B. Gate turn-off switch (GTO)
- C. Light-activated silicon-controlled rectifier (LASCR)
- D. All of the above
241. How many pn junction does SCRs have?
- A. Two
- B. Four
- C. Three
- D. Five
242. The silicon-controlled switch (SCS) is similar in construction to the
- A. triac.
- B. diac.
- C. SCR.
- D. 4-layer diode.
243. Which of the following devices has nearly the same turn-on time as turn-off time?
- A. SCR
- B. GTO
- C. SCS
- D. LASCR
244. Which of the following is (are) the advantages of the SCS over a corresponding SCR?
- A. Reduced turn-off time
- B. Increased control and triggering sensitivity
- C. More predictable firing situation
- D. All of the above
245. An effect that reduces the possibility of accidental triggering of the SCS.
- A. Miller effect
- B. Rate effect
- C. End effect
- D. Flywheel effect
246. An SCR whose state is controlled by the light falling upon a silicon semiconductor layer of the device.
- A. SCS
- B. GTO
- C. Thyristor
- D. LASCR
247. Power electronics deals with the control of ac power at what frequencies essentially?
- A. 20 KHz
- B. 1000 KHz
- C. Frequencies less than 10 Hz
- D. 60 Hz frequency
248. To turn on the UJT, the forward bias on emitter diode should be _____ the peak point voltage.
- A. more than
- B. less than
- C. equal to
- D. twice
249. What is the resistance of a certain 4-layer diode in the forward-blocking region if VAK = 15V and IA = 1 uA
- A. 15 Ω
- B. 21.21 MΩ
- C. 15 M Ω
- D. 10.61 MΩ
250. What is the peak-point voltage for the UJT in problem 76 if VBB = 15V?
- A. 10.605
- B. 5.76912
- C. 6.46915
- D. 0.8125
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