MCQs in Industrial Electronics: Principles and Applications Part VI

This is the Multiples Choice Questions Part 6 of the Series in Industrial Electronics: Principles and Applications as one of the Electronics Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

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:

Industrial Electronics Principles and Applications MCQs

PART 1: MCQs from Number 1 – 50                        Answer key: PART I

PART 2: MCQs from Number 51 – 100                   Answer key: PART II

PART 3: MCQs from Number 101 – 150                 Answer key: PART III

PART 4: MCQs from Number 151 – 200                 Answer key: PART IV

PART 5: MCQs from Number 201 – 250                 Answer key: PART V

PART 6: MCQs from Number 251 – 300                 Answer key: PART VI

Continue Practice Exam Test Questions Part VI of the MCQs Series

Choose the letter of the best answer in each questions.

251. The SCR is turned-off when the anode current falls below

• A. forward current rating
• B. breakover voltage
• C. holding current
• D. latching current

252. When an SCR is combined to a switch, it is considered as a _____ switch.

• A. bidirectional
• B. mechanical
• C. unidirectional
• D. omnidirectional

253. The p-type emitter of a UJT is _____ doped

• A. lightly
• B. moderately
• C. heavily
• D. not

254. An SCR is a _____ triggered device.

• A. current
• B. power
• C. voltage
• D. noise

255. Anode current in a thyristor is made up of:

• A. Electrons only
• B. Electrons or holes
• C. Electrons and holes
• D. Holes only

256. Once a DIAC is conducting, the only way to turn it off is with:

• A. a positive gate voltage
• B. a negative gate voltage
• C. low-current dropout
• D. breakover

257. The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of _____ in the quotation.

• A. SCR
• B. UJT
• C. Transistor
• D. SCS

258. To turn off the SCR, which of the following is done?

• A. Reduce gate voltage to zero
• B. Reverse bias the gate
• C. Reduce anode voltage to zero
• D. Reduce cathode voltage to zero

259. Your boss has asked you to recommend a thyristor that will enable you to turn it on with a pulse and also turn it off with a pulse. Which of the following should you recommend?

• A. an SCR
• B. an SCS
• C. a PUT
• D. a triac

260. The current from that semiconductor device when it is reversed biased.

• A. maximum forward current
• B. maximum forward gate current
• C. holding current
• D. leakage current

261. What is the range of the turn-on times in high-power SCR devices?

• A. 30 µs to 100 µs
• B. 10 µs to 25 µs
• C. 5 µs to 8 µs
• D. 1 µs to 5 µs

262. You need to design a relaxation oscillator circuit. The most likely device to use might be

• A. an SCR.
• B. a UJT.
• C. a triac.
• D. a 4-layer diode.

263. The ________ can be externally programmed to turn on at a desired anode-to-gate voltage level.

• A. UJT
• B. PUT
• C. SCR
• D. SCS

264. It is the minimum current which must pass through a circuit in order for it to remain in the 'ON' state.

• A. leakage current
• B. ac current
• C. holding current
• D. switching current

265. What is that value of current below which the SCR switches from the conduction state to the forward blocking region under stated conditions?

• A. Holding current
• B. Forward current
• C. Reverse current
• D. Trigger current

266. A diac is turned on by

• A. breakover voltage
• B. gate current
• C. gate voltage
• D. anode current

267. You have a light-dimmer circuit using an SCR. In testing the circuit, you find that I_G = 0 mA and the light is still on. You conclude that the trouble might be one of the following:

• A. the SCR is open.
• B. the switch is faulty.
• C. the gate circuit is shorted.
• D. this is normal; nothing is wrong.

268. Which equation defines the intrinsic standoff ratio (η) of UJTs?

• A. R_B1 / (R_B1 + R_B2)
• B. (R_B1 + R_B2) / R_B1
• C. (R_B1 + R_B2) / R_B2
• D. R_B1 + R_B2

269. The voltage across an SCR when it is turned on is about

• A. 0.5 V
• B. 0.1 V
• C. 1 V
• D. 5 V

270. The typical turn-off time of an SCR is about

• A. 20 to 40 μs
• B. 5 to 40 μs
• C. 1 to 5 μs
• D. 15 to 25 μs

271. Which of the following devices has the smallest turn-off time?

• A. SCR
• B. GTO
• C. SCS
• D. LASCR

272. A triac is equivalent to two SCRs

• A. in parallel
• B. in inverse-parallel
• C. in series
• D. in inverse-series

273. It is the phase angle relative to the power line at which point the gate is fired to commit the anode to conduct to the cathode

• A. right angle
• B. reverse angle
• C. conduction angle
• D. firing angle

274. It is the total resistance of the silicon bar from one end to another with emitter terminal open.

• A. gate resistance
• B. base resistance
• C. emitter resistance
• D. interbase resistance

275. Holding current of a thyristor is:

• A. Less than latching current
• B. More than latching current
• C. Equal to latching current
• D. Zero

276. An SCR is a solid state equivalent of which tube?

• A. Triode
• B. Gas-filled triode
• C. Pentode
• D. Tetrode

277. What is the typical turn-on time of an SCR?

• A. 1 μs
• B. 5 μs
• C. 10 μs
• D. 3 μs

278. An SCR is a solid state equivalent of which tube?

• A. Triode
• B. Gas-filled triode
• C. Pentode
• D. Tetrode

279. It is a special type of thyristor, which is a high-power semiconductor device but are fully controllable switches which can be turned on and off by their third lead.

• A. PUT
• B. MCT
• C. SCS
• D. GTO

280. When the temperature increases, the inter-base resistance of a UJT

• A. Remains unchanged
• B. Increases
• C. Decreases
• D. is zero

281. When checking a good SCR or TRIAC with an ohmmeter it will:

• A. show high resistance in both directions
• B. show low resistance with positive on anode and negative on cathode, and high resistance when reversed
• C. show high resistance with negative on anode and positive on cathode, and low resistance when reversed
• D. show low resistance in both directions

282. The UJT may be used as

• A. an amplifier
• B. a rectifier
• C. a sawtooth generator
• D. a multivibrator

283. A resistor connected across the gate and cathode of an SCR in a circuit increases its

• A. dv/dt rating
• B. Holding current
• C. Noise Immunity
• D. Turn-off time

284. AC power in a load can be controlled by connecting

• A. two SCRs in series
• B. two SCRs in parallel
• C. two SCRs in parallel opposition
• D. two SCRs in series opposition

285. An SCR combines the feature of

• A. a rectifier and resistance
• B. a rectifier and capacitor
• C. a rectifier and transistor
• D. a rectifier and inductor

286. It is voltage-controlled fully controllable thyristor similar in operation with GTO but it has a voltage controlled insulated gate.

• A. PUT
• B. MCT
• C. UJT
• D. MGT

287. The three terminals of a triac are

• A. drain, source, gate
• B. two main terminals and a gate terminal
• C. cathode, anode and gate
• D. anode, source, gate

288. A triac can pass a portion of _____ half cycle through the load

• A. only positive
• B. only negative
• C. both positive and negative
• D. neither positive nor negative

289. When the SCR is OFF, the current in the circuit is

• A. exactly zero
• B. large leakage current
• C. small leakage current
• D. thermal current

290. What is a three terminal device used to control large current to a load?

• A. SCR
• B. SCS
• C. GTO
• D. Thyristor

291. What Greek word which means “switch”?

• A. Ristor
• B. Trans
• C. Thy
• D. Thyristor

292. The ________ can conduct current in either direction and is turned on when a breakover voltage is exceeded.

• A. SCR
• B. Diac
• C. SCS
• D. Triac

293. A resistor connected across the gate and cathode of an SCR increases its:

• A. Turn off time
• B. Holding current
• C. Noise immunity
• D. dv/dt rating

294. Like an SCR, it is also a four layer device but with a gate connected to the N-region adjacent to the anode.

• A. TRIAC
• B. PUT
• C. DIAC
• D. SCS

295. An SCR is made of silicon and not germanium because silicon.

• A. is inexpensive
• B. has low leakage current
• C. is mechanically strong
• D. is tetravalent

296. The triac is fundamentally a/an _____ with a gate terminal for controlling the turn-on conditions of the bilateral device in either direction.

• A. SCR
• B. Quadric
• C. Shockley Diode
• D. Diac

297. An opto-isolator contains _____.

• A. an infrared LED
• B. a photodetector
• C. both an infrared LED and a photodetector
• D. None of the above

298. Which of the following devices is unquestionably of the greatest interest today?

• A. SCR
• B. GTO
• D. LASCR
• D. SCS

299. In a UJT maximum value of charging resistance is associated with:

• A. Peak point
• B. Valley point
• C. Any point between peak and valley point
• D. After the valley point

300. When the firing angle of SCR is increased, its output

• A. decreases
• B. increases
• C. remains unchanged
• D. doubles

Complete List of MCQs in Electronics Engineering per topic

Series of Multiple Choice Questions in Electronics Engineering

---