Electronics Engineering Multiple Choice Questions and Answers (MCQs) Part 5:

198. Which one of the following devices can be turned ‘ON’ or ‘OFF’ by applying gate signal ?

(a) SCR.
(b) SCS.
(c) TRIAC.
(d) UJT.

Answer : (a) SCR.


199. The uncontrolled electronic switch employed in power electronic converters is

(a) thyristor.
(b) bipolar Junction transistor.
(c) diode.
(d) MOSFET.

Answer : (d) MOSFET.


200. In a thyristor controlled reactor, the firing angle of thyristor is to be controlled in the range of

(a) 0 to 90°.
(b) 0 to 180°.
(c) 90 to 180°.
(d) 90 to 270°.

Answer : (b) 0 to 180°.


201. In a single-phase full-wave controlled bridge rectifier, minimum output voltage and maximum output voltage are obtained at which conduction angles ?

(a) 0°, 180° respectively.
(b) 180°, 0° respectively.
(c) 0°, 0 ° respectively.
(d) 180°, 180° respectively.

Answer : (b) 180°, 0° respectively.


202. When the firing angle α of a single-phase, fully controlled rectifier feeding constant dc current into a load is 30°, the displacement power factor to the rectifier is

(a) 1.
(b) 0.5.
(c) 1/√3.
(d) √3/2.

Answer : (d) √3/2.


203. In a single-phase semiconverter with resistive load and for a firing angle α, each SCR conduction and freewheeling action takes place respectively, for

(a) α, 0°.
(b) π – α, α.
(c) π + α, α.
(d) π – α, 0°.

Answer : (b) π – α, α.


204. A freewheeling diode in a phase-controlled rectifier

(a) improves the line power factor.
(b) is responsible for additional reactive power.
(c) prevents inverse operation.
(d) is responsible for additional harmonics.

Answer : (c) prevents inverse operation.


205. A four quadrant operation requires

(a) two full converters in series.
(b) two full converters connected back to back.
(c) two full converters connected in parallel.
(d) two semiconverters connected back to back.

Answer : (b) two full converters connected back to back.


206. A power chopper converts

(a) ac to dc.
(b) dc to dc.
(c) dc to ac.
(d) ac to ac.

Answer : (b) dc to dc.


207. Which one of the following is the most suitable device for a dc-to­-dc converter ?

(a) BJT.
(b) GTO.
(c) MOSFET.
(d) Thyristor.

Answer : (b) GTO.


208. A step-down chopper is operated in the continuous conduction mode in steady state with a constant duty ratio D. If V0 is the magnitude of the dc output voltage and if Vs is the magnitude of the input voltage, the ratio V0/Vs is given by

(a) D.
(b) 1 – D.
(c) 1 / 1 – D.
(d) D /1 – D.

Answer : (a) D.


209. In a dc chopper, if TON is the ON period and f, the chopping frequency, the output voltage in terms of input voltage, Vs, is given by

(a) VSTON/f
(b) VSf/TON
(c) VS/fTON
(d) VSfTON

Answer : (d) VSfTON


210. A step-up chopper has source voltage and duty cycle of V and a. The output voltage of this chopper is

(a) V/1 – α
(b) V(1 – α)
(c) V/(1 + α)
(d) V(1 + α)

Answer : (a) V/1 – α


211. For a step input, the output of an integrator is

(a) a pulse.
(b) a triangular waveform
(c) a spike.
(d) a ramp.

Answer : (d) a ramp.


212. A clipper circuit always

(a) needs a dc source.
(b) clips some part of the input signal.
(c) clips upper portion of input signal.
(d) clips both half cycles of input signal.

Answer : (b) clips some part of the input signal.


213. The primary function of a clamper circuit is to

(a) introduce a dc level into ac signal.
(b) suppress variations in signal voltage.
(c) raise +ve half cycle of the signal.
(d) lower -ve half cycle of the signal.

Answer : (a) introduce a dc level into ac signal.


214. Consider the following statements:

A damper circuit

1. adds or subtracts a dc voltage to or from a waveform.
2. does not change the shape of the waveform.
3. amplifies the waveform.

Which of the statements given above are correct?

(a) 1 and 2.
(b) 2 and 3.
(c) 1 and 3.
(d) 1, 2 and 3.

Answer : (a) 1 and 2.


215. Precision diode can be used as

(a) half wave rectifier.
(b) full wave rectifier.
(c) clipper and damper.
(d) all of the above.

Answer : (d) all of the above.


216. Which of the following regions of operation are mainly responsible for heating of the transistor under switching operation?

1. Saturation region.
2. Cut-off region.
3. Transition from saturation to cut-off.
4. Transition from cut-off to saturation.

Codes:

(a) 1 and 2.
(b) 2 and 3.
(c) 3 and 4.
(d) 1 and 3.

Answer : (d) 1 and 3.


217. The primary switching delay in an over-driven bipolar junction transistor is contributed by which one of the following characteristics of the transistor ?

(a) Storage time.
(b) Fall time.
(c) Rise time.
(d) Charging time.

Answer : (a) Storage time.


218. A transistor is operated as a non-saturated switch to eliminate

(a) storage time.
(b) turn-off time.
(c) turn-on time.
(d) delay time.

Answer : (b) turn-off time.


219. A relaxation oscillator is one which

(a) has two stable states.
(b) oscillates continuously.
(c) relaxes indefinitely.
(d) produces nonsinusoidal output.

Answer : (d) produces nonsinusoidal output.


220. An astable multivibrator can be used as

(a) squaring circuit.
(b) comparator.
(c) frequency-to-voltage converter.
(d) voltage-to-frequency converter.

Answer : (a) squaring circuit.


221. A monostable multivibrator

(a) has both the states as stable states.
(b) makes transition from one state to another when the trigger is applied.
(c) has both the states as unstable states.
(d) has one stable state and one quasi-stable state.

Answer : (d) has one stable state and one quasi-stable state.


222. The output time period of a transistorised monostable multivibrator using base resistor Rb and coupling capacitor Cb for the output transistor is given by

(a) RbCb
(b) 0.69 RbCb
(c) 2 RbCb
(d) 1.38 RbCb

Answer : (b) 0.69 RbCb


223. One shot multivibrator, with a pulse input gives an output:

(a) a single triangular pulse.
(b) a square pulse.
(c) an impulse.
(d) a single sinusoid pulse.

Answer : (b) a square pulse.


224. The type of multivibrator used for generation of clock pulses is

(a) monostable multivibrator.
(b) astable multivibrator.
(c) bistable multivibrator.
(d) none of the above.

Answer : (a) monostable multivibrator.


225. The purpose of Schmitt trigger circuit is to generate a

(a) triangular wave.
(b) sawtooth wave.
(c) sinusoidal wave.
(d) square wave.

Answer : (d) square wave.


226. Consider the following statements:

In order to generate square wave from a sinusoidal input signal one can use

1. Schmitt trigger circuit.
2. Clippers and amplifiers.
3. Monostable multivibrators.

Which of the above statements is/are correct

(a) 1 alone.
(b) 1 and 2.
(c) 2 and 3.
(d) 1, 2 and 3.

Answer : (a) 1 alone.


227. Narrow pulses with adjustable mark to space ratio can be obtained from square wave input signal by using which of the following ?

1. Schmitt trigger
2. Monostable multivibrator
3. Clippers

Select the correct answer using the codes given below :

(a) Only 1
(b) Only 2
(c) 1 and 2
(d) 2 and 3

Answer : (b) Only 2


228. Why is the term ‘planar technology’ for fabrication of devices in ICs used?

(a) The variety of manufacturing processes by which devices are fabricated, takes place through a single plane.
(b) The aluminium contacts to the collector, base and emitter regions of the transistors in the ICs are laid in the same plane.
(c) The collector, base and emitter regions of the transistors in ICs are laid in the same plane.
(d) The device looks like a thin plane wafer.

Answer : (a) The variety of manufacturing processes by which devices are fabricated, takes place through a single plane.


229. Ultraviolet radiation is used in IC fabrication process for

(a) diffusion.
(b) masking.
(c) isolation.
(d) metalization.

Answer : (b) masking.


230. Why is silicon dioxide (SiO2) layer used in ICs ?

(a) To protect the surface of the chip from external contaminants and to allow for selective formation of the n and p regions by diffusion.
(b) Because it facilitates the penetration of the desired impurity by diffusion.
(c) To control the concentration of the diffused impurities.
(d) Because of its high heat conduction.

Answer : (a) To protect the surface of the chip from external contaminants and to allow for selective formation of the n and p regions by diffusion.


231. In integrated circuits, the design of electronic circuits is based on the approach of use of

(a) maximum number of resistors in the circuit.
(b) large sized capacitor.
(c) minimum chip area irrespective of the type of components in the design.
(d) use of only bipolar transistors.

Answer : (c) minimum chip area irrespective of the type of components in the design.


232. Which of the following capacitors are made use of widely for a capacitance application in monolithic ICs?

1. MOS capacitor.
2. Collector-Substrate capacitor.
3. Collector-Base capacitor.
4. Base-Emitter capacitor.

Select the correct answer using the code given below :

(a) 1 and 2 only.
(b) 2 and 3 only.
(c) 3 and 4 only.
(d) 1 and 4 only.

Answer : (a) 1 and 2 only.


233. The process of extension of a single-crystal surface by growing a film in such a way that the added atoms form a continuation of the single-crystal structure is called

(a) ion implantation.
(b) chemical vapour depiction.
(c) electroplating.
(d) Epitaxy.

Answer : (d) Epitaxy.


234. Op-amps have become very popular because

(a) they are very cheap.
(b) they are extremely small in size.
(c) their external characteristics can be altered to suit any application.
(d) they are available in different packages.

Answer : (c) their external characteristics can be altered to suit any application.


235. An operational amplifier is basically a

(a) low gain ac amplifier.
(b) high gain dc amplifier.
(c) high gain RC coupled amplifier.
(d) low gain transformer-coupled amplifier.

Answer : (b) high gain dc amplifier.


236. The ideal op-amp is an ideal

(a) voltage controlled current source.
(b) voltage controlled voltage source.
(c) current controlled current source.
(d) current controlled voltage source.

Answer : (b) voltage controlled voltage source.


237. The ideal op-amp has the following characteristics.

(a) Ri = ∞, A = ∞, R0 = 0
(b) Ri = 0, A = ∞, R0 = 0
(c) Ri = ∞, A = ∞, R0 = ∞
(d) Ri = 0, A = ∞, R0 = ∞

Answer : (a) Ri = ∞, A = ∞, R0 = 0


238. An ideal OP-AMP is used to make an inverting amplifier. The two input terminals of the OP-AMP are at the same potential because

(a) the two input terminals are directly shorted internally.
(b) the input impedance of the OP-AMP is infinity.
(c) the open loop gain of the OP-AMP is infinity.
(d) CMRR is infinity.
(e) both (c) and (d).

Answer : (e) both (c) and (d).


239. The purpose of phase lag compensation is to

(a) make the op-amp stable at very high values of gain.
(b) make the op-amp stable at very low values of gain.
(c) reduce the unity gain frequency.
(d) increase the bandwidth.

Answer : (c) reduce the unity gain frequency.


240. The voltage gain of an ideal voltage follower is

(a) 1
(b) <1
(c) 0
(d) infinity

Answer : (a) 1