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Module 04.(B1) Electronic Fundamentals
1.1a. Semiconductors - Diodes.
Question Number.1.What gives the colour of an LED?.Option A.The
active element.Option B.The plastic it is encased in.Option C.The
type of gas used inside it.Correct Answer is.The active
element.Explanation.The active element is the element used in the
doping of the semiconductor material. Aircraft Electricity and
Electronics 5th Edition Eismin Page 121.
Question Number.2.A germanium diode is used for.Option
A.rectification.Option B.voltage stabilization.Option
C.modulation.Correct Answer is.rectification.Explanation.Germanium
diode has the least forward bias voltage drop and is best for
rectification.
Question Number.3.Why is a diode put in parallel with an
LED?.Option A.To protect it from AC.Option B.So it will work only
above a certain voltage.Option C.So it will work only below a
certain voltage.Correct Answer is.To protect it from
AC.Explanation.An LED has a high forward bias voltage drop but is
easily damaged when reverse biased. AC is therefore not good for an
LED.
Question Number.4.When testing the forward bias of a diode with
a multimeter.Option A.the positive lead of the ohmmeter is placed
on the anode.Option B.it does not matter which terminal the
positive lead of the ohmeter is placed.Option C.the positive lead
of the ohmmeter is placed on the cathode.Correct Answer is.the
positive lead of the ohmmeter is placed on the anode.Explanation.To
test forward bias, the positive lead of the multimeter must be
placed on the anode. Note: If the question says 'moving coil meter'
then it would be the negative lead on the anode, since the negative
side of the battery in such a meter is connected to the + lead.
Aircraft Electricity and Electronics 5th Edition Eismin Page
113.
Question Number.5.This is a diagram of.
Option A.an SCR.Option B.a TRIAC.Option C.a Schottky
diode.Correct Answer is.an SCR.Explanation.NIL.
Question Number.6.Which of the following describes the
characteristics of a Thyristor?.Option A.High voltage
handling.Option B.High power handling.Option C.High current
handling.Correct Answer is.High current handling.Explanation.A
thyristor (such as an SCR) is a high current switching.
Question Number.7.Light Emitting Diodes (LEDs).Option A.emit
light of only one wavelength dependent on type.Option B.have very
wide viewing angles.Option C.are easily damaged if forward biased b
more than 5V.Correct Answer is.emit light of only one wavelength
dependent on type.Explanation.NIL.
Question Number.8.In a semiconductor junction diode, electrons
are the minority carriers.Option A.within the P region.Option
B.within the N region.Option C.in both the N and P regions.Correct
Answer is.within the P region.Explanation.NIL.
Question Number.9.A silicon diode, when compared to a germanium
diode has.Option A.a higher forward bias voltage.Option B.the same
forward bias voltage.Option C.less forward bias voltage.Correct
Answer is.a higher forward bias voltage.Explanation.Si = 0.6V, Ge =
0.2V. Aircraft Electricity and Electronics 5th Edition Eismin Page
111.
Question Number.10.This symbol is.
Option A.a transistor.Option B.a diode.Option C.a triac.Correct
Answer is.a diode.Explanation.NIL.
Question Number.11.This symbol is.
Option A.a photodiode.Option B.a laser diode.Option C.an
LED.Correct Answer is.a photodiode.Explanation.The photodiode is
used in reverse bias. The minority current increases when light
shines on it.
Question Number.12.A zener diode.Option A.allows current to flow
in one direction.Option B.stabilizes voltage at a predetermined
level.Option C.acts like a switch.Correct Answer is.stabilizes
voltage at a predetermined level.Explanation.Zener diodes are
usually used in voltage regulator circuits. Aircraft Electricity
and Electronics 5th Edition Eismin Page 385.
Question Number.13.A junction diode.Option A.is similar to a
vacuum diode but cannot rectify.Option B.has one p-n
junction.Option C.can handle only very small currents.Correct
Answer is.has one p-n junction.Explanation.NIL.
Question Number.14.Reverse bias.Option A.raises the potential
barrier.Option B.lowers the potential barrier.Option C.greatly
increases the majority carrier current.Correct Answer is.raises the
potential barrier.Explanation.NIL.
Question Number.15.A diode connected across a relay coil is used
to.Option A.dissipate coil spikes on switch off.Option B.allow the
coil to energize with only one polarity.Option C.cause a delay in
switching on.Correct Answer is.dissipate coil spikes on switch
off.Explanation.Aircraft Electricity and Electronics 5th Edition
Eismin Page 121 reading material.
Question Number.16.To check the forward resistance of a diode
with a multimeter, the lead connected to the positive terminal is
put to the.Option A.anode.Option B.cathode.Option C.either anode or
cathode.Correct Answer is.anode.Explanation.To forward bias a diode
with a multimeter, the positive lead must be connected to the
anode. Note: If it were a moving coil meter, you must connect the
negative lead to the anode since the positive end of the battery is
connected to the negative lead.
Question Number.17.A thyristor has which of the
following?.Option A.A positive temperature coefficient.Option
B.High resistance when switched off.Option C.High resistance when
switched on.Correct Answer is.High resistance when switched
off.Explanation.The thyristor (such as an SCR or TRIAC) is
basically a switch which provides a high resistance when switched
off.
Question Number.18.What does the circuit shown do?.
Option A.Full wave rectifier.Option B.Half wave rectifier.Option
C.Voltage doubler.Correct Answer is.Half wave
rectifier.Explanation.The diagram shows a half wave rectifier. The
capacitor is for smoothing the output. A full wave rectifier
requires 4 diodes and a voltage doubler requires two
capacitors.
Question Number.19.In an LED, what is used to make the
colour?.Option A.The plastic lens cover.Option B.The
electrons.Option C.The doping material.Correct Answer is.The doping
material.Explanation.The dopant is what gives the LED its
colour.
Question Number.20.An atom with 5 electrons in its outer shell
is part of.Option A.a C type material.Option B.a P type
material.Option C.an N type material.Correct Answer is.an N type
material.Explanation.An atom with five electrons in its outer shell
(pentavalent) will provide an extra free electron and make the
material an N type. Aircraft Electricity and Electronics 5th
Edition Eismin Page 110.
Question Number.21.A thyristor is commonly used for.Option
A.overvolts regulation.Option B.voltage regulation.Option
C.rectification.Correct Answer is.rectification.Explanation.A
thyristor (especially an SCR) is often used for rectification.
Question Number.22.A diode which emits photons when conducting
is a.Option A.light emitting.Option B.varactor.Option
C.zener.Correct Answer is.light emitting.Explanation.Photons =
light, so a diode which emits light is a Light Emitting Diode.
Question Number.23.The electrodes of an SCR are.Option A.gate,
cathode, anode.Option B.source, drain, gate.Option C.anode,
cathode, source.Correct Answer is.gate, cathode,
anode.Explanation.The electrodes of an SCR are the anode, cathode
and the gate. Aircraft Electricity and Electronics 5th Edition
Eismin Page 120.
Question Number.24.What gives an LED its colour?.Option A.A
gas.Option B.The cover.Option C.Composition and impurity of the
compound.Correct Answer is.Composition and impurity of the
compound.Explanation.It is the doping element which gives an LED
its colour.
Question Number.25.Forward voltage of a silicon diode is.Option
A.1.6V.Option B.0.6V.Option C.0.2V.Correct Answer
is.0.6V.Explanation.Si = 0.6V, Ge = 0.2V Aircraft Electricity and
Electronics 5th Edition Eismin Page 111 or 113.
Question Number.26.What is the typical volts drop across an
LED.Option A.0.2V.Option B.0.4V.Option C.1.6V.Correct Answer
is.1.6V.Explanation.An LED volts drop is typically 1.6 - 2.4V.
Aircraft Electricity and Electronics 5th Edition Eismin Page
121.
Question Number.27.What diode gives off light photons when
forward biased.Option A.LED.Option B.Gunn diode.Option C.Schottky
diode.Correct Answer is.LED.Explanation.LEDs give off light
(photons) when forward biased.
Question Number.28.The anode of a diode is connected to a +4V DC
supply and the cathode is connected to a +2V DC supply. The diode
is.Option A.forward biased not conducting.Option B.reverse biased
not conducting.Option C.forward biased conducting.Correct Answer
is.forward biased conducting.Explanation.Forward bias is anode to
cathode. 4V fwd bias and 2V reverse bias, the diode is 2V fwd bias
in total.
Question Number.29.Using electron flow in a diode the current
flows from.Option A.Anode to Cathode.Option B.Cathode to
Base.Option C.Cathode to Anode.Correct Answer is.Cathode to
Anode.Explanation.ELECTRON FLOW (i.e. American notation) is cathode
to anode (against the arrow direction). Aircraft Electricity and
Electronics 5th Edition Eismin Page 111.
Question Number.30.When a hole diffuses from the p region to the
n region.Option A.raises the potential barrier.Option B.it becomes
a minority carrier in the n region.Option C.lowers the potential
barrier.Correct Answer is.raises the potential
barrier.Explanation.The potential barrier is formed by holes
diffusing from the P region to the N region, (and electrons
diffusing from the N region to the P region).
Question Number.31.A junction diode.Option A.can handle only
small currents.Option B.is similar to a vacuum diode but cannot
rectify.Option C.has one p-n junction.Correct Answer is.has one p-n
junction.Explanation.A junction diode is so named for its one
junction. Aircraft Electricity and Electronics 5th Edition Eismin
Page 111.
Question Number.32.A germanium diode.Option A.has a lower
forward bias voltage than a silicon diode.Option B.has a higher
forward bias voltage than a silicon diode.Option C.has the same
forward bias voltage as a silicon diode.Correct Answer is.has a
lower forward bias voltage than a silicon diode.Explanation.Forward
bias voltage of germanium diode = 0.2 V. Silicon diode = 0.6 V.
Aircraft Electricity and Electronics 5th Edition Eismin Page
111.
Question Number.33.What switches off a thyristor?.Option
A.Reverse bias gate.Option B.Remove the gate voltage.Option
C.Remove supply voltage.Correct Answer is.Remove supply
voltage.Explanation.To switch off a thyristor (such as an SCR) you
must disconnect the supply voltage. Aircraft Electricity and
Electronics 5th Edition Eismin Page 120.
Question Number.34.When an SCR is switched on it has.Option
A.low resistance.Option B.no change in resistance.Option C.high
resistance.Correct Answer is.low resistance.Explanation.An SCR is
basically a switch, which, when switched on has a low resistance.
Aircraft Electricity and Electronics 5th Edition Eismin Page
120.
Question Number.35.What type of pulse is required to switch on
an SCR?.Option A.Positive.Option B.Negative.Option C.Positive or
negative.Correct Answer is.Positive.Explanation.A positive pulse is
required to switch an SCR on.
Question Number.36.A piece of pure Germanium.Option A.is
electrically stable.Option B.has a deficit of electrons.Option
C.has an excess of electrons.Correct Answer is.is electrically
stable.Explanation.In a solid piece of semiconductor material, all
the valence electrons are occupied in the covalent bond. It does
not conduct electricity. Aircraft Electricity and Electronics 5th
Edition Eismin Page 110.
Question Number.37.When a diode is forward biased, current flow
is mainly due to the.Option A.germanium bias junction.Option
B.majority carriers.Option C.minority carriers.Correct Answer
is.majority carriers.Explanation.Forward bias = majority
carriers.
Question Number.38.When a diode is forward biased the.Option
A.positive lead is connected to both N and P type.Option B.positive
lead is connected to the N type and negative to the P type.Option
C.positive lead is connected to the P type and negative to the N
type.Correct Answer is.positive lead is connected to the P type and
negative to the N type.Explanation.To forward biased, connect
Positive to P, Negative to N. Aircraft Electricity and Electronics
5th Edition Eismin Page 117.
Question Number.39.The typical voltage drop across an L.E.D
is.Option A.2V.Option B.4V.Option C.6V.Correct Answer
is.2V.Explanation.2V typical.
Question Number.40.What are the majority carriers for a forward
biased PN junction device?.Option A.Electrons and holes.Option
B.Holes.Option C.Electrons.Correct Answer is.Electrons and
holes.Explanation.Majority carriers are electrons in the N
material, and holes in the P material.
Question Number.41.Germanium in its pure state is.Option
A.negatively charged.Option B.neutral.Option C.positively
charged.Correct Answer is.neutral.Explanation.Both germanium and
silicon are neutrally charged, even when doped. Aircraft
Electricity and Electronics 5th Edition Eismin Page 110.
Question Number.42.Which diode has a lower forward bias
voltage?.Option A.Silicon.Option B.Germanium.Option C.Both have the
same forward bias voltage.Correct Answer
is.Germanium.Explanation.Silicon about 0.6V, Germanium about 0.2V.
Aircraft Electricity and Electronics 5th Edition Eismin Page
111.
Question Number.43.A Zener diode is used for.Option A.voltage
stabilisation.Option B.rectification.Option C.voltage
regulation.Correct Answer is.voltage regulation.Explanation.A Zener
diode is used for voltage regulation. Aircraft Electricity and
Electronics 5th Edition Eismin Page 120.
Question Number.44.A thyristor SCR is a.Option A.bi-directional
device.Option B.unidirectional device.Option C.multidirectional
device.Correct Answer is.unidirectional
device.Explanation.http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/diac.html#c4
Question Number.45.What component is used to turn AC to
DC?.Option A.Thyristor.Option B.Diode.Option C.Transistor.Correct
Answer is.Diode.Explanation.Although a thyristor (SCR) can be used,
a diode is more common. Aircraft Electricity and Electronics 5th
Edition Eismin Page 113.
Question Number.45.What component is used to turn AC to
DC?.Option A.Thyristor.Option B.Diode.Option C.Transistor.Correct
Answer is.Diode.Explanation.Although a thyristor (SCR) can be used,
a diode is more common. Aircraft Electricity and Electronics 5th
Edition Eismin Page 113.
Question Number.46.What is an intrinsic material?.Option A.One
with added elements.Option B.One with removed elements.Option C.A
pure material.Correct Answer is.A pure
material.Explanation.Intrinsic is a pure material.
Question Number.47.The voltage drop of a silicon diode is.Option
A.1 V.Option B.0.7 V.Option C.0.3 V.Correct Answer is.0.7
V.Explanation.Aircraft Electricity and Electronics 5th Edition
Eismin Page 111.
Question Number.48.A diode is parallel to an LED in an AC
circuit to.Option A.provide correct amount of current for LED when
circuit is switched on.Option B.prevent back EMF in the circuit
when LED is switched off.Option C.protect LED from AC current when
switched on.Correct Answer is.protect LED from AC current when
switched on.Explanation.The negative half cycle of the AC must be
bypassed around the LED.
Question Number.49.In a forward biased diode, current is carried
by.Option A.majority carriers.Option B.both.Option C.minority
carriers.Correct Answer is.both.Explanation.Forward bias is both,
reverse bias is minority carriers only.
Question Number.50.When checking a diode for reverse bias
resistance the positive lead goes to.Option A.anode and negative
lead to earth.Option B.cathode and negative lead to anode.Option
C.anode and negative lead to cathode.Correct Answer is.cathode and
negative lead to anode.Explanation.Positive lead to cathode.
Question Number.51.Zener diodes are used for.Option A.Current
control.Option B.Voltage control.Option C.Temperature
control.Correct Answer is.Voltage
control.Explanation.Comment/Reference (if available).
Question Number.52.Once started conducting an SCR switches
off.Option A.only when the anode goes negative to the
cathode.Option B.automatically after a specific time.Option C.only
when the anode goes positive to the cathode.Correct Answer is.only
when the anode goes negative to the cathode.Explanation.NIL.
Question Number.53.In a forward biased diode, electrons leave
the.Option A.the anode.Option B.the cathode.Option C.the doped
area.Correct Answer is.the
cathode.Explanation.explainAnswer[3]="Electrons jump accross the
depletion layer from the Cathode (-ve) to the Anode (+ve) to
recombine with the holes and close the depletion layer".
Question Number.54.Diodes are.Option A.conductors.Option
B.semi-conductors.Option C.Insulators.Correct Answer
is.semi-conductors.Explanation.Only answer which is correct in both
bias configurations.
Question Number.55.To function, i.e. conduct, a junction diode
made of silicon requires a forward bias of at least.Option
A.0.2V.Option B.1.41V.Option C.1V.Correct Answer
is.1V.Explanation.Silicon diodes require around 0.7V, so a is the
closest.
Question Number.56.What is the average gain of an Op Amp?.Option
A.20.Option B.200,000.Option C.200.Correct Answer
is.200,000.Explanation.NIL.http://en.wikipedia.org/wiki/Op_amp#DC_behavior
1.1b. Semiconductors - Diodes.
Question Number.1.Tunnel diodes have the following
characteristics.Option A.Heavily doped P-N junction with an
extremely narrow depletion region.Option B.Lightly doped P and N
regions and a high reverse breakdown voltage.Option C.Lightly doped
P region, heavily doped N region and has a fast response
time.Correct Answer is.Heavily doped P-N junction with an extremely
narrow depletion
region.Explanation.NIL.http://en.wikipedia.org/wiki/Tunnel_diode
Question Number.2.The capacitance of a varactor diode is.Option
A.inversely proportional with reverse bias voltage.Option B.a
linear function of applied reverse bias voltage.Option C.directly
related to the forward bias voltage.Correct Answer is.inversely
proportional with reverse bias
voltage.Explanation.NIL.http://en.wikipedia.org/wiki/Varactor_diode
Question Number.3.A semiconductor doped with an element having a
valency of 5 will produce.Option A.an N type material.Option
B.either an N type or a P type depending on what type of
semiconductor material is used.Option C.a P type material.Correct
Answer is.an N type material.Explanation.Pentavalent materials make
an N type material due to its extra electron. Aircraft Electricity
and Electronics 5th Edition Eismin Page 110.
Question Number.4.In a diode clamper, if the resistor is removed
making the time constant equal to C x r where r is the reverse
resistance of the diode, this will ensure a.Option A.long time
constant.Option B.short time constant.Option C.Very Long Time
Constant.Correct Answer is.long time constant.Explanation.NIL.
Question Number.5.PIN diodes are used mainly for.Option A.linear
rectifiers.Option B.fast switching devices.Option C.voltage
operated rectifiers.Correct Answer is.fast switching
devices.Explanation.NIL.
Question Number.6.To enable an IMPATT diode to operate
correctly, it must be.Option A.connected to a resonant
circuit.Option B.used in its reverse bias mode.Option C.operated in
its negative resistance range.Correct Answer is.operated in its
negative resistance range.Explanation.NIL.
Question Number.7.What type of diode would be used to stop
voltage spikes across a coil of a relay?.Option A.Gunn diode.Option
B.Double acting diode.Option C.Schottky diode.Correct Answer
is.Double acting
diode.Explanation.NIL.http://en.wikipedia.org/wiki/Voltage_stabiliser,
http://en.wikipedia.org/wiki/Zener_diode
Question Number.8.What is a schottky diode used for?.Option
A.Rectification.Option B.Stabilization.Option C.Very high frequency
applications.Correct Answer is.Very high frequency
applications.Explanation.A schottky diode has very little junction
capacitance and can be used for very high frequency switching
applications.
Question Number.9.When a hole diffuses from a p-region to the
n-region it.Option A.becomes a minority carrier in the
n-region.Option B.lowers the potential barrier.Option C.raises the
potential barrier.Correct Answer is.raises the potential
barrier.Explanation.This is descriptive of holes crossing the PN
junction to form the depletion layer. Aircraft Electricity and
Electronics 5th Edition Eismin Page 111.
Question Number.10.The junction barrier offers opposition to
only.Option A.holes in the p-region.Option B.free electrons in the
n-region.Option C.majority carriers in both regions.Correct Answer
is.majority carriers in both
regions.Explanation.NIL.http://en.wikipedia.org/wiki/P-n_junction
Question Number.11.Avalanche breakdown occurs when.Option
A.reverse bias exceeds a certain value.Option B.forward bias
exceeds a certain value.Option C.forward current becomes
excessive.Correct Answer is.reverse bias exceeds a certain
value.Explanation.Reverse biasing a diode will cause avalanche
breakdown at a certain value. Aircraft Electricity and Electronics
5th Edition Eismin Page 120.
Question Number.12.If forward bias is increased from zero on a
p-n junction, a rapid increase in current flow for a relatively
small increase in voltage occurs.Option A.when the flow of minority
carriers is sufficient to cause an avalanche breakdown.Option
B.when the depletion layer becomes larger than the space charge
area.Option C.only after the forward bias exceeds the potential
barrier.Correct Answer is.only after the forward bias exceeds the
potential barrier.Explanation.A forward biased PN junction will
conduct only when the forward bias voltage exceeds the junction
barrier - i.e Si = 0.6V, Ge = 0.2V.
Question Number.13.A band pass filter excludes
frequencies.Option A.below the frequency required only.Option
B.above and below the frequency required.Option C.above the
frequency required only.Correct Answer is.above and below the
frequency required.Explanation.A band-pass filter excludes
frequencies above and below a particular frequency. Aircraft
Electricity and Electronics 5th Edition Eismin Page 288.
Question Number.14.In an unbiased p-n junction, current flow
is.Option A.zero, because equal but opposite currents are crossing
the junction.Option B.zero, because no charges are crossing the
junction.Option C.due to the diffusion of minority carriers
only.Correct Answer is.zero, because no charges are crossing the
junction.Explanation.NIL.
Question Number.15.With a small amplitude voltage, what type of
diode would you use to produce the output waveform?.Option
A.Gunn.Option B.Zener.Option C.Schottky.Correct Answer
is.Schottky.Explanation.The first part of the device is a basic RC
differentiator, providing positive and negative pulses from the
square wave input. The diode blocks the negative pulses. Since the
amplitude is small, a fast acting diode with a low forward bias
voltage is required. The Schottky diode fits the bill. Question
Number.16.What diode is used to stop power spikes in a coil?.Option
A.Gunn diode.Option B.Schottky diode.Option C.Two directional zener
diode.Correct Answer is.Two directional zener diode.Explanation.A
two directional zener diode (actually 2 zener diodes back-to-back)
is used to stop power spikes.
Question Number.17.What type of diode when forward biased holes
and electrons recombine producing photons?.Option A.LED.Option
B.Photodiode.Option C.Gunn.Correct Answer is.LED.Explanation.The
word 'photons' implies light emission - i.e. a light emitting diode
(LED).
Question Number.18.A zener diode is designed to operate.Option
A.below its breakdown voltage.Option B.either above or below its
breakdown voltage.Option C.above its breakdown voltage.Correct
Answer is.above its breakdown voltage.Explanation.A zener diode is
designed to operate above its breakdown voltage continuously.
Aircraft Electricity and Electronics 5th Edition Eismin Page
120.
Question Number.19.A triac is a type of.Option
A.thermistor.Option B.transistor.Option C.thyristor.Correct Answer
is.thyristor.Explanation.Thyristors include, SCRs, Triacs and
diacs. Aircraft Electricity and Electronics 5th Edition Eismin Page
120.
Question Number.20.If a junction diode is reverse biased too
far, the output current would.Option A.reverse direction.Option
B.cease to flow.Option C.increase.Correct Answer
is.increase.Explanation.If a junction diode is reverse biased too
far, it will 'breakdown' and a high current will flow.
Question Number.21.When a PN junction is forward biased, it
conducts via.Option A.intrinsic carrier.Option B.majority
carrier.Option C.minority carrier.Correct Answer is.majority
carrier.Explanation.Forward biased - majority carriers.
Question Number.22.In the Zener Diode suppressor shown, point X
in respect to point Y should be.
Option A.more Positive.Option B.either positive or
negative.Option C.more negative.Correct Answer is.more
negative.Explanation.A Zener Diode is always wired in reverse bias.
Aircraft Electricity and Electronics 5th Edition Eismin Page
138.
Question Number.23.If the reverse bias voltage across a diode is
too high.Option A.load current reduces to zero.Option B.load
current increases rapidly.Option C.load current reverses.Correct
Answer is.load current increases rapidly.Explanation.If the reverse
bias voltage is too high, the diode will break down and pass
current.
Question Number.24.An LED which emits green light uses.Option
A.gallium phosphide.Option B.gallium arsenide.Option C.gallium
arsenide phosphide.Correct Answer is.gallium
phosphide.Explanation.NIL.http://www.oksolar.com/led/led_color_chart.htm
Question Number.25.An LED which emits red light uses.Option
A.gallium phosphide.Option B.gallium arsenide phosphide.Option
C.gallium arsenide.Correct Answer is.gallium arsenide
phosphide.Explanation.NIL.
Question Number.26.A photodiode is operated under.Option
A.reverse bias conditions.Option B.forward bias conditions.Option
C.reverse or forward bias conditions.Correct Answer is.reverse bias
conditions.Explanation.NIL.http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/photdet.html#c2
Question Number.27.To increase capacitance of a varactor
diode.Option A.reverse bias voltage is increased.Option B.reverse
bias voltage is decreased.Option C.forward bias voltage is
decreased.Correct Answer is.reverse bias voltage is
decreased.Explanation.NIL.http://www.tpub.com/content/neets/14179/css/14179_131.htm
Question Number.28.The diagram shows a.
Option A.voltage doubler.Option B.half wave rectifier.Option
C.full wave rectifier.Correct Answer is.voltage
doubler.Explanation.NIL.http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/voldoub.html
Question Number.29.A bi-directional TRIAC has two SCRs connected
in.Option A.series parallel.Option B.inverse parallel.Option
C.parallel series.Correct Answer is.inverse
parallel.Explanation.NIL.http://en.wikipedia.org/wiki/TRIAC
Question Number.30.A thyristor can be forward biased by a.Option
A.positive or negative pulse.Option B.negative pulse.Option
C.positive pulse.Correct Answer is.positive
pulse.Explanation.Positive pulse only.
Question Number.31.N' type materials are doped with.Option
A.acceptors.Option B.acceptors and donors.Option C.donors.Correct
Answer is.donors.Explanation.N' type materials have excess
electrons, therefore the impurity element is a donor of electrons.
Aircraft Electricity and Electronics 5th Edition Eismin Page
110.
Question Number.32.In an electronic circuit, if the anode of a
diode is clamped to ground. What is this called?.Option A.A
negative clamping circuit.Option B.A negative limiting
circuit.Option C.A positive clamping circuit.Correct Answer is.A
positive clamping circuit.Explanation.NIL.
Question Number.33.To decrease the capacitance of a
varactor.Option A.reverse bias should be decreased.Option B.forward
bias should be increased.Option C.reverse bias should be
increased.Correct Answer is.reverse bias should be
increased.Explanation.NIL.
Question Number.34.A Zener diode is used across the output for a
power supply circuit to.Option A.give a full wave
rectification.Option B.prevent thermal runway.Option C.provide a
steady DC voltage output without falling.Correct Answer is.provide
a steady DC voltage output without falling.Explanation.A Zener
diode is the main component in a voltage regulator.
Question Number.35.If a diode has gone open circuit in a full
wave bridge rectifier, the output frequency ripple is.Option A.the
same as the input frequency.Option B.twice the input
frequency.Option C.half the input frequency.Correct Answer is.the
same as the input frequency.Explanation.A fully serviceable bridge
rectifier produces an output ripple twice the input frequency. If
one diode goes open circuit, one of the output 'humps' drops to
zero.
Question Number.36.In a full wave bridge rectifier.Option A.the
output is pure DC. Frequency is 0 Hz.Option B.the output frequency
is twice the input frequency.Option C.the output voltage is twice
the input voltage.Correct Answer is.the output is pure DC.
Frequency is 0 Hz.Explanation.The output is un-smoothed DC of 2 x
input frequency.
Question Number.37.After passing through a rectifier,
alternating current becomes.Option A.smooth direct current.Option
B.pulsating direct current.Option C.square wave form
current.Correct Answer is.pulsating direct
current.Explanation.Assuming the rectifier does not contain any
smoothing circuitry.
Question Number.38.A Zener diode usually works.Option A.only in
reverse bias.Option B.at variable voltages.Option C.only in forward
bias.Correct Answer is.only in reverse bias.Explanation.NIL.
Question Number.39.P' type materials require.Option
A.acceptors.Option B.conductors.Option C.donors.Correct Answer
is.acceptors.Explanation.NIL.http://en.wikipedia.org/wiki/P-type_semiconductor
Question Number.40.Which of the following explains how the
photodiode works?.Option A.Photodiodes are forward biased to
conduct when light falls upon them.Option B.Photodiodes are back
biased not to conduct when light falls upon them.Option
C.Photodiodes are back biased to conduct when light falls upon
them.Correct Answer is.Photodiodes are back biased to conduct when
light falls upon
them.Explanation.NIL.http://en.wikipedia.org/wiki/Photodiodes
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