 # MCQ in Industrial Electronics Part 6 | ECE Board Exam

(Last Updated On: August 8, 2018) 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.

### MCQ Topic Outline included in ECE Board Exam Syllabi

• MCQ in Industrial Electronics
• MCQ in Electronic Control System
• MCQ in Industrial Solid State Services
• MCQ in Welding Systems
• MCQ in Thyristors
• MCQ in High Frequency Heating
• MCQ in Feedback Systems / Servomechanism
• MCQ in Transducers
• MCQ in Motor Speed Control Systems
• MCQ in Robotic Principles
• MCQ in Bioelectrical Principles
• MCQ in Instrumentation and Control

### Continue Practice Exam Test Questions Part 6 of the 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

Solution:

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

A. bidirectional

B. mechanical

C. unidirectional

D. omnidirectional

Solution:

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

A. lightly

B. moderately

C. heavily

D. not

Solution:

254. An SCR is a ___________ triggered device.

A. current

B. power

C. voltage

D. noise

Solution:

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

A. Electrons only

B. Electrons or holes

C. Electrons and holes

D. Holes only

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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.

Solution:

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

Solution:

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

Solution:

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

Solution:

266. A diac is turned on by

A. breakover voltage

B. gate current

C. gate voltage

D. anode current

Solution:

267. You have a light-dimmer circuit using an SCR. In testing the circuit, you find that IG = 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.

Solution:

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

A. RB1 / (RB1 + RB2)

B. (RB1 + RB2) / RB1

C. (RB1 + RB2) / RB2

D. RB1 + RB2

Solution:

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

Solution:

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

Solution:

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

A. SCR

B. GTO

C. SCS

D. LASCR

Solution:

272. A triac is equivalent to two SCRs

A. in parallel

B. in inverse-parallel

C. in series

D. in inverse-series

Solution:

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

Solution:

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

Solution:

275. Holding current of a thyristor is:

A. Less than latching current

B. More than latching current

C. Equal to latching current

D. Zero

Solution:

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

A. Triode

B. Gas-filled triode

C. Pentode

D. Tetrode

Solution:

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

A. 1 μs

B. 5 μs

C. 10 μs

D. 3 μs

Solution:

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

A. Triode

B. Gas-filled triode

C. Pentode

D. Tetrode

Solution:

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

Solution:

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

A. Remains unchanged

B. Increases

C. Decreases

D. is zero

Solution:

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

Solution:

282. The UJT may be used as

A. an amplifier

B. a rectifier

C. a sawtooth generator

D. a multivibrator

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

A. SCR

B. SCS

C. GTO

D. Thyristor

Solution:

291. What Greek word which means “switch”?

A. Ristor

B. Trans

C. Thy

D. Thyristor

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

C. Shockley Diode

D. Diac

Solution:

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

Solution:

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

A. SCR

B. GTO

D. LASCR

D. SCS

Solution:

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

Solution:

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

A. decreases

B. increases

C. remains unchanged

D. doubles

Solution:

### Questions and Answers in Industrial Electronics

Following is the list of multiple choice questions in this brand new series:

MCQ in Industrial Electronics Principles and Applications
PART 1: MCQ from Number 1 – 50                        Answer key: PART 1
PART 2: MCQ from Number 51 – 100                   Answer key: PART 2
PART 3: MCQ from Number 101 – 150                 Answer key: PART 3
PART 4: MCQ from Number 151 – 200                 Answer key: PART 4
PART 5: MCQ from Number 201 – 250                 Answer key: PART 5
PART 6: MCQs from Number 251 – 300                 Answer key: PART 6
PART 7: MCQ from Number 301 – 350                 Answer key: included

### Complete List of MCQs in Electronics Engineering per topic

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