PAST GCE QUESTIONS AND SOLUTIONS MCQ POWER ELECTRONICS TVE CAMEROON

PAST GCE QUESTIONS TVE FOR POWER ELECTRONICS

CAMEROON GENERAL CERTIFICATE OF EDUCATION BOARD

Technical and Vocational Education Examinations

Electrical Power Systems EPS (F3)

Note here that the years will not be disclosed.  These are the most recent years past questions.

SETTINGS 1

1.             The circuit of figure 1 can be referred to as that of

A	voltage step down
B	current step down
C	voltage step up
D	current step up

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2.           DIACs are specifically designed to trigger;

A	TRIACs
B	Thyristors
C	GTO
D	TRIACs and Thyristors

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3.           A thyristor can be;

A	Turned ON by applying a gate pulse and turned OFF only when current becomes zero
B	Turned ON and turned OFF by applying gate pulse
C	Turned ON by applying a gate pulse and turned OFF by removing the gate pulse
D	Turned ON by making current non zero and turned OFF by making current zero

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4.           If the firing angle of a rectifier becomes negative then, the rectifier begins to work as;

A	A negative Rectifier
B	An inverter
C	A chopper
D	A regulator

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5.           Which of the following statements is correct for the advantage of an all thyristor bridge over an all diode bridge?           

A	The all thyristor bridge has a better power factor
B	The all thyristor bridge is asymmetrical
C	The all thyristor bridge is uncontrollable
D	The all thyristor bridge can control power consumed by a load

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6.           In the filtered half-wave rectification circuit, the minimum peak inverse voltage (V_RM) rating of the diode should be  _______  the peak voltage of the source.   

A	equal to
B	2 times
C	√2 times

D

0.5 time

7.          The primary function of the capacitor in the rectifier circuit of figure 2 is to: 

A	Minimize variations in a.c. input signal
B	Suppress harmonics rectified output
C	Remove ripples from the rectifier output
D	Stabilize DC output voltage

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8.           A rectifier which requires four diodes is:  

A	Half wave voltage doubler
B	Full wave voltage doubler
C	Full wave bridge circuit
D	Voltage quadrupler

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9.           Power electronics essentially deals with control of ac power at frequency:       

A	Above 20KHz
B	Above 1000KHz
C	Less than 10Hz
D	Equal to 50Hz

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10.      The role of the diode in the chopper circuit of figure 3 is to overcome:

A	Current variation frequency
B	Rapid frequency change
C	Voltage surge during closing and opening of H
D	Voltage drop

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11.         Silicon is preferred for the manufacturing of semi-conductor components because it

A	Is relatively cheap
B	Needs lower doping level
C	Has higher temperature and current capacity
D	Has lower breakdown voltage

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12.         Avalanche breakdown is primarily dependent on the phenomenon of

A	Collision
B	Doping
C	Ionization
D	Recombination

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13.         The output of a half wave rectifier is suitable only for

A	Charging of car radios
B	Running of ac motors
C	Charging batteries
D	Running tape recorders

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14.        14.     Which of the following approximations is often used in electronics circuit?

A	Ic ≈ Ie
B	Ib ≈ Ic
C	Ib ≈ Ie
D	Ie ≈ Ic + Ib

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15.         In a BJT, largest current flow occurs

A	In the emitter
B	In the collector
C	In the base
D	Through CB junction

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16.         Improper biasing of a transistor circuit leads to

A	Excessive heat production at collector terminal
B	Distortion in output signal
C	Faulty location of load line
D	Heavy loading of emitter terminal.

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17.         A FET consist of a

A	Source
B	Drain
C	Gate
D	All of the above

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18.        Consider figure 4, the period of the load voltage  (V_L) is ;

A	D1 and D3 conducts
B	D2 and D4 conducts
C	D1 conducts and D3 doesn’t conduct
D	D1 doesn’t conduct D4 conducts

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19.    The circuit of figure 5 protects the thyristor against:       

A	Variation in current
B	Variation in voltage
C	Variation temperature
D	Against overvoltage

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20.         The ripple factor of a bridge rectifier is 

A	0.406
B	0.812
C	1.21
D	1.11

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21.         A rectifier circuit with four diodes is

A	Full-wave center tapped rectifier
B	Half wave rectifier
C	Full wave bridge rectifier
D	Half-wave center tapped rectifier

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22.         During thyristor application(s), its firing conditions are or is given by            

A	VAK less than zero
B	iG less than zero
C	VAK and iG less than zero
D	VAK and iG greater than zero

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23.         For a non controlled rectification of acronym PD3 has how many diodes?

A	6
B	4 and a thyristor
C	4
D	3

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24. Consider the three phase half wave rectification chronograms from an oscilloscope of load R of figure 6. During manipulation of the Oscilloscope, it was regulated to 5v/division. What is the maximum value of each line voltage?

A	30V
B	30√3V
C	60V
D	60√3V

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25.         An inverter is

A	an ac/dc converter
B	an ac/ac converter
C	a dc/ac converter
D	a dc/dc converter

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26.         The form factor of a waveform is defined as the ratio of its

A	average value to its r.m.s. value
B	r.m.s. value to its average value
C	peak value to r.m.s value
D	peak value to average value

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27.         A resistor used to discharge a filter capacitor when the power supply is turned off is called a

A	load resistor
B	current resistor
C	bleeder resistor
D	surge resistor

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28.        In the circuit of figure 7, the reverse voltage across each diode is expressed as    

A	(2√V)/2R
B	(V√2)/2
C	(2√V)/π
D	2V√2

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29.         The area within a semiconductor diode where no mobile current carriers exist when it is formed is called  region.

A	depletion
B	saturation
C	potential barrier
D	space charge

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30.         In semi-conductors, depletion layer is the region where

A	recombination
B	ionization
C	thermal energy
D	doping

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31.         When a bipolar junction transistor operates in cut-off,

A	VCE = 0
B	VCE = VCC
C	VCE has negative value
D	IC is maximum

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32.         The ripple factor of an output of a rectifier

bridge can considerably be reduced by using

A	a thyristor
B	a transformer
C	a capacitor
D	a MOSFET

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33.         A thyristor is preferred to a transistor for the manufacture of chopper switches because it

A	cannot be easily destroyed
B	has a high chopping frequency
C	can be triggered by small gate current
D	can control heavy power loads

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34.         The voltage at the terminal of a d.c. motor which is supplied by a series chopper of duty ration 0.25 when connected to a 220V d.c. supply is

A	55V
B	165V
C	220V
D	275V

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35.         What is the duty cycle of a chopper?

A	Ton/Toff
B	Ton/T
C	T/Ton
D	Toff x Ton

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36.         The expression of the average output voltage for a series (step down) chopper with an output voltage (E) and duty ratio α is

A	V = E/α
B	V = αE
C	V = 2E/α
D	V= 2E/απ

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37.         A full wave uncontrolled rectifier is made of:

A	A bridge of diodes.
B	One diode
C	One thyristor
D	A bridge of thyristors

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38.         A thyristor is a:

A	Three terminals, four layers PNPN material.
B	Three terminals, three layers PNP material.
C	Four terminals, four layers NPNP material.
D	Three terminals, three layers NPN material.

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39.         The waveform of the figure 8 above is that of the voltage across the resistive load of :

A	Full wave controlled rectification
B	A full wave uncontrolled rectification
C	Single phase controlled rectification
D	Single phase uncontrolled rectification

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40.         Which rectifier requires four diodes?

A	Half wave voltage doubler
B	Full wave bridge circuit
C	Full wave voltage doubler
D	Voltage quadrupler

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41.         A transistor series voltage regulator is called emitter follower regulator because the emitter of the pass transistor follows the ____________ voltage.

A	Base
B	Input
C	Output
D	Collector

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42.         When BJT is employed as an amplifier it operates

A	Over the active region
B	In saturation
C	Well into saturation
D	In cut – off

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43.         The r.m.s value of a half wave rectified current is 10A, its value for full wave rectification will be   

A	20A
B	(20/π) A
C	14.14A
D	(40/π) A

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44.         Which of the following semiconductor materials has a threshold voltage of 0.7V?

A	arsenic
B	germanium
C	boron
D	silicon

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45.         Electronic shell distribution of a Si atom is

A	2, 8, 4
B	2, 10, 2
C	2, 7, 5
D	2, 4, 8

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46.         During forward biased operation, a diode

A	blocks current
B	drops a large voltage
C	has a high resistance
D	conducts current

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47.         A chopper can be defined as an electronic device which converts a constant

A	alternating current to a variable alternating
B	direct current to a variable alternating current.
C	alternating current to a variable direct current
D	direct current to a variable direct current

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48.         When a transistor is fully switched ON, it is said to be

A	Shorted
B	Open
C	Saturated
D	Cut – off

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49.         When a BJT is in saturation

A	Ic = 0
B	Vce = 0
C	Ib controls Ic
D	Vce has positive value

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50.         The r.m.s. value of a sinusoidal alternating current is equal to its instantaneous value at an angle of

A	60°
B	90°
C	30°
D	45°

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NOW GO BACK AND CHECK YOUR WORK