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ELEX > ESD > Flashcards

ESD Flashcards

1
Q

A diode rectifier with a C filter will have average output voltage _____ than that obtained by a rectifier without the C filter.

A. higher than
B. lower than
C. none of these choices
D. same as

A

A. higher than

C filter improves the efficiency and
eliminates ripples, thus increasing the
average value of the output waveform.

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2
Q

In a regulated power supply, the output
of the rectifier is connected to the _____

A. transformer
B. output
C. Filter
D. regulator

A

C. Filter

The ‘Rectifier’ (diodes) converts AC into ‘pulsating DC’ which is then smoothed out into pure DC by a ‘Filter’ (often simply a capacitor).
The blocks in a Regulated Power
Supply: Input, Transformer,
Rectifier, Filter, Regulator, Output

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3
Q

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. a PUT
C. a triac
D. an Scs

A

D. an Scs

The Silicon Controlled Switch (SCS) is a power semiconductor device similar to an SCR, but it is designed to turn off
when a positive voltage/input current
pulse is applied to an additional “Anode
gate” terminal.

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4
Q

In a power supply, which stage follows
the rectifier?

A. filter
B. output
C. regulator
D. transformer

A

A. filter

The blocks in a Regulated Power
Supply: Input, Transformer, Rectifier,
Filter, Regulator, Output.

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5
Q

Which of the following part is used in construction of DC machine but not in AC machine?

A. Shaft
B. Armature Winding
C. Field winding
D. Commutator

A

D. Commutator

Commutator is used in mechanical
rectification process, to convert induced
AC to output DC. In AC machine, we
don’t need rectification process.

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6
Q

The armature of DC motor is laminated to _____

A. To reduce inductance
B. To reduce hysteresis loss
C. To reduce mass
D. To reduce eddy current loss

A

D. To reduce eddy current loss

The armature is built up in a cylindrical or drum shape high grade silicon steel in form of lamination. By using
laminations, the circular path of eddy currents is terminated. Hence heating and ultimately damage to the armature can be reduced by lamination.

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7
Q

Efficiency of center taped full wave
rectifier is

A. 40.6%
B. 50%
C. 81.2%
D. 45.3%

A

C. 81.2%

Efficiency of a rectifier is the
effectiveness of rectifier to convert AC
to DC. For half wave rectifier it is only
40.6% while for a full-wave rectifier it is 81.2%.

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8
Q

What is the typical dropout voltage for
the 7812 fixed positive voltage
regulator?

A. 100 mV
B. 1.5V
C. 2V
D. 4 mV

A

C. 2V

The dropout voltage is the difference
between the output voltage and the
input voltage at which the circuit quits
regulation with further reductions in
input voltage.

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9
Q

The change in output voltage for the
corresponding change in load current in
a 7805 IC regulator is defined as

A. All of these choices
B. Line regulation
C. Input regulation
D. Load regulation

A

D. Load regulation

Load regulation is defined as the
change in output voltage for a change in
load current and is also expressed in
millivolts or as a percentage of output
voltage.

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10
Q

An ideal voltmeter has _____
equivalent resistance and ideal
ammeter has _____ resistance.

A. Zero, infinite
B. Unity, Unity
C. Zero, Zero
D. Infinite, Zero

A

D. Infinite, Zero

An ideal voltmeter has Infinite equivalent resistance and ideal ammeter has zero equivalent resistance.

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11
Q

Among the following, the most suitable
method to turn on the SCR device is
the …

A. forward voltage triggering method
B. temperature triggering method
C. dv/dt triggering method
D. gate triggering method

A

D. gate triggering method

(A) & (B) are unreliable methods
(C) can permanently damage the SCR
(D) Gate triggering is simple, reliable &most efficient.

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12
Q

Each cell of a fully charged six lead acid
cell battery produces:

A. 1.2 volts
B. 2.1 volts
C. 1.75 volts
D. 4.2 volts

A

B. 2.1 volts

Each lead acid cell produces 2.1 volts.

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13
Q

Among the dc motors, which produces
the highest torque?

A. shunt
B. compound
C. series
D. differentially compounded

A

C. series

DC series motor produces the largest
torque.

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14
Q

Which of the following devices has
nearly the same turn-on time as turn-off
time?

A. SCR
B. GTO
C. LASCR
D. SCS

A

B. GTO

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15
Q

A cell, that can be repeatedly recharged by supplying it with electrical energy, is known as a:

A. memory cell
B. primary cell
C. storage cell
D. low leakage cell

A

D. low leakage cell

A ‘storage cell’ can be recharged
repeatedly. A ‘primary cell’, such as a
common Zinc-Carbon flashlight cell, can
only be used once.

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16
Q

For the SCR to remain in the ON
(conducting) state

A. negative gate signal is continuously
required
B. gate signal is continuously required
C. no forward anode-cathode voltage is
required
D. no continuous gate signal is required

A

D. no continuous gate signal is required

Unlike the transistor devices, once the
SCR is turned on by the gate terminal,
the gate terminal losses its control over
the device.

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17
Q

It is defined as the ratio of dc power
delivered to the load to ac
power rating of a transformer

A. PRF
B. Efficiency
C. TUF
D. Power Regulation

A

B. Efficiency

The transformer utilization factor (TUF)
of a rectifier circuit is defined as the
ratio of the DC power available at the
load resistor to the AC rating of the
secondary coil of a transformer.

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18
Q

From the two transistor (T1 & T2)
analogy of SCR, the total anode current of SCR is _____ in the equivalent circuit.

A. the sum of both the collector current
B. the sum of base current of T1 & collector
current of T2
C. the sum of both the base currents
D. the sum of base current of T2 & collector
current of T1

A

A. the sum of both the collector current

The sum of both the collector currents
of T1 and T2 forms the total anode
current of SCR. Refer the model.

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19
Q

In the SCR structure the gate terminal is
located…

A. in between the anode & cathode terminal
B. near the anode terminal
C. none of these choices
D. near the cathode terminal

A

D. near the cathode terminal

The gate is located near the
cathode, because it allows fast
turning on of the device when the gate signal is applied by forward basing the second junction.

(ESD FIGURE)

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20
Q

You have the schematic diagram of
several types of circuits. Which of these
circuits most likely uses a triac?

A. an amplifier
B. a programmable oscillator
C. an ac motor control
D. an oscillator

A

C. an ac motor control

Triac is a bilateral/bidirectional device.
It can conduct in either directions of
current flow, therefore it is most likely used in controlling the flow of current for AC loads

21
Q

The D’Arsonval- movement can be converted into audio frequency ac ammeter by adding a

A. thermocouple
B. chopper
C. rectifier
D. transducer

A

C. rectifier

Since a D’Arsonval meter movement can
only respond to DC current, the AC
parameter to be measured needs to be
converted first to DC using a rectifier
circuit.

22
Q

A measure of consistency or
repeatability of measurements is called

A. boldness
B. precision
C. correctness
D. accuracy

A

B. precision

Precision refers to consistency or
repeatability or measurements while
accuracy refers to the exactness of
measured value to the expected value.

23
Q

_____ device from the thyristor
family has its gate terminal connected
to the n-type material near the anode.

A. PUT
B. SCR
C. SUS
D. GTO

A

A. PUT

PUT is Programmable Unijunction
Transistor which is a p-n-p-n device just like the SCR with its gate connected to the n-type material.

24
Q

During the positive half-cycle of the
input voltage in a bridge rectifier,

A. all diodes are forward-biased
B. two diodes are forward-biased
C. all diodes are reverse-biased
D. one diode is forward-biased

A

B. two diodes are forward-biased

Full-wave bridge rectifier has 4 diodes,
with 2 out of four diodes conducting
(forward-baised) for each alternation of
the AC input.

25
Q

You need a very efficient thyristor to
control the speed of an AC fan motor. A
good device to use would be

A. a BJT
B. a 4-layer diode
C. a PUT
D. a triac

A

D. a triac

Since the load is AC, the needed
thyristor must be bidirectional or
bilateral. Among the options given, only
the triac has the ability to conduct in
both directions.

26
Q

Which instrument is used to measure
electric current?

A. An ammeter
B. An ohmmeter
C. A voltmeter
D. A wattmeter

A

A. An ammeter

Ohmmeter - used to measure
Resisance
Wattmeter - used to measure Power
Voltmeter - used to measure
Voltage
Ammeter - used to measure Current

27
Q

Identify the symbol:

(ESD FIGURE)

A. SCS
B. triac
C. PUT
D. SCR

A

C. PUT

(ESD FIGURE)

28
Q

Refer to the given figure. This circuit is
known as…

(ESD FIGURE)

A. a step-up switching regulator
B. a series-pass voltage regulator
C. a step-down switching regulator
D. a shunt voltage regulator

A

D. a shunt voltage regulator

29
Q

In DC motors, direction of rotation of is
determined by _____

A. Lenz’s law
B. Faraday’s law
C. Coulomb’s law
D. Fleming’s hand rule

A

D. Fleming’s hand rule

Flemings laws can be summarized as whenever, a current carrying conductor comes under a magnetic field, there will be a force acting on the conductor and on the other hand, if a conductor is forcefully brought under a magnetic
field, there will be an induced current in
that conductor.

30
Q

How many terminals does a 78XX
series IC regulator have?

A. 8
B. 4
C. 2
D. none of these choices

A

D. none of these choices

(ESD FIGURE)

31
Q

Why field winding of a DC series motor
is provided with thick wire?

A. In order to reduce eddy current to provide
large flux
B. To provide large flux
C. As it carries large load current
D. To reduce the of insulting materials

A

C. As it carries large load current

In DC series motor, the cross-sectional area of wire used for field coils has to be large because the in this case field coils carry the load or armature current.As the cross-sectional area is large, the resistance is minimum and series
voltage drop is also minimum.

32
Q

Identify the symbol: (1)

(ESD FIGURE)

A. PUT
B. SCR
C. SCS
D. LASCR

A

C. SCS

33
Q

In an ordinary thyristor…

A. turn on and turn off times are equal
B. turn on time is more than turn off time
C. turn on time may be equal, less than or
more than turn off time
D. turn off time is more than turn on time

A

D. turn off time is more than turn on time

34
Q

The minimum value of anode current below which it must fall to completely turn-off the device is called as the

A. holding current value
B. peak anode current value
C. latching current value
D. switching current value

A

A. holding current value

35
Q

The specified maximum junction
temperature of thyristors is about

A. 200°C
B. 80°℃
C. 50°C
D. 120C

A

D. 120C

36
Q

In a DC motor, the commutator serves as a _____

A. mechanical rectifier for alternating EMF to
direct EMF
B. all of these choices
C. none of these choices
D. mechanical inverter to invert the direct
applied voltage to alternating voltage

A

D. mechanical inverter to invert the direct
applied voltage to alternating voltage

A DC motor is equivalent to an AC
machine plus a mechanical inverter, i.e,
commutator.

37
Q

In this improved series regulator circuit which of the following components is the sampling circuit?

(ESD FIGURE)

A. Resistors R1 and R2
B. Load resistor
C. Zener diode
D. Either of the two transistors Q1 or Q2

A

A. Resistors R1 and R2

38
Q

The 7912 regulator IC provides

A. 12V
B. -5V
C. -12V
D. 5V

A

C. -12V

39
Q

What is the typical value of the
triggering anode gate for SCS devices?

A. 15A
B. 1A
C. 150 A
D. 1.5 mA

A

D. 1.5 mA

40
Q

dv/dt protection is provided to the SCR
by…

A. connecting a capacitor in parallel with the
load
B. connecting an inductor & resister in
parallel with the device
C. connecting a capacitor & resister in
parallel with the device
D. connecting an inductor in series with the
load

A

C. connecting a capacitor & resister in
parallel with the device

Snubber circuit R-C in parallel with SCR
is connected for dv/dt protection.

41
Q

The GTO can be turned off

A. by a negative anode-cathode voltage
B. by removing the gate pulse
C. by a negative gate pulse
D. by a positive gate pulse

A

C. by a negative gate pulse

The GTO can be turned off by applying a
negative gate pulse to the gate terminal.

42
Q

Error in voltmeter reading is due to

A. battery aging
B. insertion
C. conversion
D. loading

A

D. loading

Errors in voltmeter is due to loading
effects; in ammeter it is due to insertion
effects; and in ohmmeter it is due to
battery voltage decay or battery aging.

43
Q

Choose the false statement.

A. SCR is a bidirectional device
B. SCR is a controlled device
C. In SCR the gate is the controlling terminal
D. SCR are used for high-power applications

A

A. SCR is a bidirectional device

SCR is a unidirectional device, current
only flows from anode to cathode.

44
Q

In a thyristor, the forward breakover
voltage

A. increases as gate current is increased
B. may be constant or may depend on gate
current
C. is constant
D. decreases as gate current is increased

A

D. decreases as gate current is increased

In thyristors, the voltage at which device
starts conduction is called as forward
break over voltage. In general, this
voltage is in the range of 50 to 500
Volts. … By increasing the gate current,the forward break over voltage occurs

45
Q

Before connecting an ohmmeter to a
circuit, you should first:

A. Install new batteries
B. Operate the circuit
C. Check the circuit with a voltmeter to
make sure the circuit is not powered
D. Set the range selector to the highest range

A

C. Check the circuit with a voltmeter to
make sure the circuit is not powered

Voltage will damage the ohmmeter.
Verify the cirucit is electrially dead.

46
Q

For the greatest accuracy, what should
be the input impedance of a VOM be?

A. 1,000 ohms/V
B. 50,000 ohms/V
C. as large as possible
D. as small as possible

A

C. as large as possible

Ideal value of voltmeter’s resistance =
infinite ohms

47
Q

Refer to the given figure. The purpose
for the zener diode D1 is

(ESD FIGURE)

A. to limit the input voltage to the circuit
B. to sense the error signal
C. to supply a reference voltage
D. to amplify the error signal

A

C. to supply a reference voltage

48
Q

The symbol in figure is for..

(ESD FIGURE)

A. SCS
B. None of these choices
C. SUS
D. SBS

A

A. SCS

(ESD FIGURE)

49
Q

During the positive half-cycle of the
input voltage in a bridge rectifier,

A. all diodes are forward-biased
B. two diodes are forward-biased
C. all diodes are reverse-biased
D. one diode is forward-biased

A

B. two diodes are forward-biased

Full-wave bridge rectifier has 4 diodes,
with 2 out of four diodes conducting
(forward-baised) for each alternation of
the AC input.

ELEX (13 decks)

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