Diodes and Applications
1.What is a varistor?
a) A voltage-dependent
b) A voltage-dependent
c) A current-dependent
d) A current-dependent
Answer: Option A
resistor
diode
resistor
diode
Explanation:
This is a resistor whose value changes with the applied voltage. We can get
this type of resistors from fets.
2.Which type of transformer is required to create a 180 degree input
to a rectifier?
a) Center-tapped secondary
b) Step-down secondary
c) Stepped-up secondary
d) Split winding primary
Answer: Option A
Explanation:
Transformer having two winding. At the secondary winding, one common
terminal is divided the winding into two equal half winding. The 1st half for
0-90 degree (+ve half cycle) and another half for 90-180 degree (-ve half
cycle). And that common terminal is called as center tapped terminal. Like
that centered tapped transformer is required for 180 degree input to rectify.
3.What circuit activity may shift a characteristic curve so that diode
operating points are different?
a) Higher power (heat)
b) Higher resistance
c) Lower voltage
d) Lower current
Explanation:
The total value of collector current is given by collector current+reverse
saturation current. For every 10 degree raise in temp the reverse saturation
current doubles thereby increasing the collector current. As the collector
current increases the diode operating point shifts towards breakdown region
which in turn increases the temperature and continuing the above process
(early effect).
4.What is wrong with this diode?
a) Open
b) Short
c) Nothing
d) Not enough data
Answer: Option C
Explanation:
Answer C is correct because diode without any input acts as a normal
component and it is in reverse bias according to connection as shown above
So reverse bias gives high resistance.
5.The dc current through each diode in a bridge rectifier equals:
a) The load current
b) Half the dc load current
c) Twice the dc load current
d) One-fourth the dc load current
Answer: Option A
Explanation:
If we use 1, 2, 3, 4 diodes, when +ve cycle of ac is appeared across diode 1,
then it will conduct and diode 2 will block full ac current then how will the
diode 3 will get +ve cycle to conduct because full ac current is blocked by
diode 2 which is connected in between diode 3 and diode 1 ?
6.When matching polarity connections have been made and the
potential difference (PD) is above 0.7 V, the diode is considered to
be:
a) Not working
b) Forward biased
c) Reverse biased
d) An open switch
Answer: Option B
Explanation:
If the positive terminal is connected with other positive terminal or negative
terminal is connected with other negative terminal it becomes an forward
bias.
7.In a power supply diagram, which block indicates a smooth dc
output?
a) Transformer
b) Filter
c) Rectifier
d) Regulator
Answer: Option D
Explanation:
Transformer : Give us AC sinusoidal wave form.
Rectifier : Convert AC into pulsating DC.
Filter : Convert Pulsating into ripples or approximate pure DC.
Regulator : Just regulate output DC voltage.
8.If a 169.7 V half-wave peak has an average voltage of 54 V, what
is the average of two full-wave peaks?
a) 119.9 V
b) 108.0 V
c) 115.7 V
d) 339.4 V
Answer: Option B
Explanation:
Half wave rectifier.
Vdc = Vpeak/pi.
For full wave rectifier.
Vdc = 2*Vdc (half wave rectifier).
54*2 = 108.
9.What is the current through the LED?
a) 0 ma
b) 23 ma
c) 18 ma
d) 13 ma
Answer: Option D
Explanation:
Led colour Forward voltage (volt).
1. Infrared 1.3 to 1.5.
2. Red 1.5 to 1.8.
3. Yellow 2 to 2.2.
4. Green 2.2 to 2.4.
5. Blue 3 to 5.
10.The characteristic curve for the complex model of a silicon diode
shows that
a) The barrier potential is 0 V
b) The barrier potential stays fixed at 0.7 V
c) The barrier potential increases slightly with an increase in
current
d) The barrier potential decreases slightly with an increase in
current
Answer: Option C
Explanation:
Lets say we have a P.N junction diode,
Lets connect it in forward bias. Ok.!
It means + of battery is connected to "P"(majority holes)
- of battery is connected to "N"(majority electrons).
So when when v increase the incoming current, electrons(-ve charge)in P
gets attracted towards the positive terminal(+)of battery and holes(+ve
charge)get attracted to Negative terminal(-ve). So the width of barrier
increases.
11.Since diodes are destroyed by excessive current, circuits must
have:
a) Higher voltage sources
b) Current limiting resistors
c) More dopants
d) Higher current sources
Answer: Option B
Explanation:
We are using the resistance to restrict the excessive flow of current through
the device. And that resistance is known as "current limiting resistor".
12.A diode for which you can change the reverse bias, and thus vary
the capacitance is called a
a) Varactor diode
b) Tunnel diode
c) Zener diode
d) Switching diode
Answer: Option A
Explanation:
A varacter diode is basically a reverse biased PN junction which utilises the
inherent capacitence of the depletion layer. It is also known as varicap,
voltcapor tunning diode. It is used as a voltage variable capacitor.
13.A filtered full-wave rectifier voltage has a smaller ripple than
does a half-wave rectifier voltage for the same load resistance and
capacitor values because:
a) There is a shorter time between peaks
b) There is a longer time between peaks
c) The larger the ripple, the better the filtering action
d) None of the above
Answer: Option A
Explanation:
If we use capacitive filter if the peaks comes quickly or to soon then
capacitor will not get full time to discharge so we will get better dc output.
If we use inductive filter then quick transition of low and high value of the
rectifier output the inductor will oppose the change.
(as inductor opposes any quick change in current across it) so we will get
the smoother output.
For better understanding please refer to the capacitive and inductive filter
for full-wave rectifier.
14.Testing a good diode with an ohmmeter should indicate
a) High resistance when forward or reverse biased
b) Low resistance when forward or reverse biased
c) High resistance when reverse biased and low resistance when
forward biased
d) High resistance when forward biased and low resistance when
reverse biased
Answer: Option C
Explanation:
In forward bias diode allow the current from the anode to cathode. In
reverse bias the diode block the current flow due to high resistance.
15.The peak inverse voltage (PIV) across a nonconducting diode in a
bridge rectifier equals approximately:
a) Half the peak secondary voltage
b) Twice the peak secondary voltage
c) The peak value of the secondary voltage
d) Four times the peak value of the secondary voltage
Answer: Option C
Explanation:
# piv for half- wave rectifier is Vm
# full-wave rectifier is 2Vm
# bridge rectifier is Vm
Because which are the entire secondary voltage appears across the nonconducting diodes
As far question option C is correct.
16.What is the current through the diode?
a) 1 ma
b) 0.975 ma
c) 0.942 ma
d) 0.0 ma
Answer: Option A
Explanation:
In case of ideal diode in forward bias voltage drop is 0.
Hence I= V/R.
I=12/12k.
=1ma.
17.Electrons in the outermost orbit or shell of an atom are called
a)
Free electrons
b)
Negative ions
c)
Valence electrons
d)
Conduction band electrons
Answer: Option C
Explanation:
You are right that electrons in conduction band are called free electrons, but
electrons in outermost orbits are valence electrons which are not free
electrons until they got energy equal to their Bandgap energy.
18.Shunting the ac component away from the load is the task of a:
a)
Transformer
b)
Filter
c)
Regulator
d)
Rectifier
Answer: Option B
Explanation:
FILTER - Removes unwanted AC component which is present in rectifier
output
REGULATOR - Regulates the O/P or in simple words maintains a stable
output.
19.A pn junction allows current flow when
a)
The p-type material is more positive than the n-type material
b)
The n-type material is more positive than the p-type material
c)
Both the n-type and p-type materials have the same potential
d)
There is no potential on the n-type or p-type materials
Answer: Option A
Explanation:
There are more holes near the depletion boundary than deeper into the nregion. Therefore they undergo a thermal diffusion, resulting in a net flux of
holes (red) away from the depletion boundary.
20.What is the current through the zener diode?
a)
0 ma
b)
7 ma
c)
8.3 ma
d)
13 ma
Answer: Option B
Explanation:
I = (Vs - Vz)/R.
= (13-6)/1.
= 7 ma.
21.When a diode is forward biased, the voltage across it
a)
Is directly proportional to the current
b)
Is inversely proportional to the current
c)
Is directly proportional to the source voltage
d)
Remains approximately the same
Answer: Option D
Explanation:
Knee voltage is that voltage which is required by silicon, Germanium, etc to
remove electrons from its last orbit and become part of conduction.
22.Why is heat produced in a diode?
a)
Due to current passing through the diode
b)
Due to voltage across the diode
c)
Due to the power rating of the diode
d)
Due to the PN junction of the diode
Answer: Option A
Explanation:
H=I2*R is the dissipated through the diode where 'R' is the bulk resistance of
the diode.
23.The arrow in the schematic symbol of a diode points to
a)
The n-type material, which is called the anode
b)
The n-type material, which is called the cathode
c)
The p-type material, which is called the anode
d)
The p-type material, which is called the cathode
Answer: Option C
Explanation:
Arrow head points to p junction means anode and bar on the other hand
represents the n side means cathode.
24.The diode schematic arrow points to the:
a)
Trivalent-doped material
b)
Positive axial lead
c)
Anode lead
d)
Cathode lead
Answer: Option D
Explanation:
->|- (cathode lead) diode schematic arrow point to the cathode lead.
25.When checking a diode, low resistance readings both ways
indicate the diode is:
a)
Open
b)
Satisfactory
c)
Faulty
d)
Not the problem
Answer: Option C
Explanation:
When diode is in forward condition then it's resistance get reduced and when
it is in reverse condition then it shows high resistance so we can say that the
diode is faulty because showing the low resistance in forward and reverse
condition.
26.In a diode schematic, the anode is represented by a(n):
a)
Triangle
b)
Vertical line
c)
Zig-zag line
d)
Element indicator
Answer: Option A
Explanation:
Triangle is represented diode.
27.An IC regulator receives an overload; it will:
a)
Shut down
b)
Compensate for heat
c)
Provide more voltage
d)
Sample and adjust
Answer: Option A
Explanation:
Main purpose of regulators are to maintain a fixed output no matters
whether input varies or not. So in case when it receives overload it should
simply sample the output voltage and adjust the o/p voltage.
Please correct me I'm wrong.
28.With full-wave rectification, current through the load resistor
must be:
a)
In opposite directions
b)
To the external load
c)
From the reverse biased diode
d)
In the same direction
Answer: Option D
29.A characteristic curve is the result of a current versus voltage
plot of diode activity, which begins at the:
a)
3rd quadrant
b)
Current plot
c)
Graph origin
d)
Voltage plot
Answer: Option C
Explanation:
He is mean to say that at 0 voltage there will be 0 current so that the graph
will start from graph origin.
30.Rectifier output polarity depends upon:
a)
Cycles of input
b)
Capacitor polarity
c)
Half or full wave
d)
Diode installation
Answer: Option D
Explanation:
Whatever the type of rectifier the voltage will be dc voltage. So 3rd option is
incorrect. Capacitor is generally used as a regulator. Therefore 2nd option is
incorrect. The polarity of output voltage depends upon direction in which
diodes are forward biased. Therefore 4th option is correct.
31.With a 12 V supply, a silicon diode, and a 370-ohm resistor in
series, what voltage will be dropped across the diode?
a)
0.3 V
b)
0.7 V
c)
0.9 V
d)
1.4 V
Answer: Option B
Explanation:
Silicon diode barrier potential is 0.7.
32.If the frequency of the applied ac signal to a half-wave rectifier is
60 Hz, the frequency of the pulsating dc output will be
a)
30 pps
b)
60 pps
c)
90 pps
d)
120 pps
Answer: Option B
Explanation:
Vs/Vp=Ns/Np
Vs=169.706*1/20
Vs=8.485v
peak output voltage=Vs-0.7=7.78v
33.What is the peak output voltage for this half-wave rectifier?
a)
1V
b)
7.8 V
c)
10.9 V
d)
15.6 V
Answer: Option B
Explanation:
V2= n2/n1*v1
=1/20*169.706
so v2=8.4853 volts
so output voltage will be 8.4853-0.7
Vo=7.7853
so option 'B' is correct 7.8 volts
34.Thermal shutdown occurs in an IC regulator if:
a)
Power dissipation is too high
b)
Internal temperature is too high
c)
Current through the device is too high
d)
Load resistance increases
Answer: Option B
35.The conduction band is closest to the valence band in
a)
Semiconductors
b)
Conductors
c)
Insulators
d)
The distance is the same for all of the above.
Answer: Option A
Explanation:
The answer should be conductors.
Conduction band energy for insulators > 5 ev.
Semiconductors 1.1 ev. Conductors 0 ev.
36.What is the percent of regulation if Vnl = 20 V and Vfl = 19.8 V?
a)
0%
b)
1%
c)
2%
d)
5%
Answer: Option B
Explanation:
Vnl=20 volt.
Vfl=19.8 volt.
SO, Percent of Regulation = (Vnl-Vfl/Vfl)*100.
= (20-19.8/19.8)*100.
= .2/19.8*100.
= 1%.
37.With a half-wave rectified voltage across the load resistor, load
current flows for what part of a cycle?
a)
0 degrees
b)
90 degrees
c)
180 degrees
d)
360 degrees
Answer: Option C
Explanation:
No current flows in negative half cycle so only for +ve half cycle it is 180.
38.Which of the following circuits would require the least amount of
filtering?
a)
A half-wave rectifier
b)
A full-wave rectifier
c)
A bridge rectifier
d)
A full-wave rectifier and a bridge rectifier
Answer: Option D
Explanation:
As the bridge rectifier do 0.48% and a full wave also 0.48% so obviosly the
one will be the answer.
39.What is wrong with this circuit?
a)
The zener is open.
b)
The zener is shorted.
c)
Nothing
d)
Not enough data
Answer: Option A
Explanation:
If the zener is opened, we have only R1 and R2 resister are in
series.Therefore now we have a battery of 24V , R1 , R2 are all in series.
Apply voltage divider rule and find the voltage across the R2.It will come
nearly 4.8v by doing calculation
i.e ., Voltage at R2=Vcc*R2/(R1+R2)
=24*2.5*10^3/(10K+2.5K)
=4.8v
This 4.8v is nearly indicated as 4.790 in the voltmeter shown in the diagram
across the 2.5kohm resistor.
This is possible only if the zener is made as open.
40.The voltage where current may start to flow in a reverse-biased
pn junction is called the
a)
Breakdown voltage
b)
Barrier potential
c)
Forward voltage
d)
Biasing voltage
Answer: Option A
Explanation:
When diode is in reversed condition, no current flows but when the reversed
voltage increases enormously, it leads to junction breakdown and hence
diode behaves as shorted path and thus high current flows through it.
41.Providing a constant output regardless of ac input or load
resistance changes is the function of a:
a)
Transformer
b)
Filter
c)
Regulator
d)
Rectifier
Answer: Option C
Explanation:
In zener diode it act as voltage ragulater & the out voltage is equal to zener
voltage so o\p is ac.
42.When a diode is destroyed it has infinite impedance. When
damaged by heat it will probably:
a)
Short
b)
Conduct more
c)
Conduct less
Open
Answer: Option A
Explanation:
Because diode has negative temperature coefficient of resistance so as temp
increases the conductivity increases thereby short circuit.
43.The area at the junction of p-type and n-type materials that has
lost its majority carriers is called the
a)
Barrier potential
b)
Depletion region
c)
N region
d)
P region
Answer: Option B
Explanation:
Because the minority carriers can't break the depletion layer.
44.DC power should be connected to forward bias a diode as follows:
a)
anode, + cathode
b)
cathode, – anode
c)
+ anode, – cathode
d)
+ cathode, + anode
Answer: Option C
45.At any given time in an intrinsic piece of semiconductor material
at room temperature
a)
Electrons drift randomly
b)
Recombination occurs
c)
Holes are created
d)
All of the above
Answer: Option D
Explanation:
At room temperature. Some covalnt bonds get breaked in intrinsic
semiconductors. So electrons and holes are created.
46.In a power supply diagram, which block indicates a pulsating dc
output?
a)
Transformer
b)
Filter
c)
Rectifier
d)
Regulator
Answer: Option C
Explanation:
Because Rectifier's output is not stable and it acts as input sinewave.
47.List three diode packages:
a)
Clip package, DIP, small current package
b)
DIP, small current package, large current package
c)
Small current package, large current package, and SIP
d)
Small current package, large current package, clip package
Answer: Option D
48.The mimicking of an open/closed switch by a diode allows
alternating current to be:
a)
Rectified
b)
Regulated
c)
Controlled
d)
Attenuated
Answer: Option A
Explanation:
As to converting from ac into dc diode with load resistance is used so it will
perform same operation.
True/False
1.A reverse biased diode will act as an open switch.
a)
True
b)
False
Answer: Option A
2.If the diode in a series circuit is reverse biased, the resistor will
drop all the applied voltage.
a)
True
b)
False
Answer: Option B
Explanation:
As diode is reverse biased so there will be no any current flow.
3.The PIV rating of a diode in a full-wave bridge rectifier is more
than that required for a full-wave center-tapped configuration.
a)
True
b)
False
Answer: Option B
Explanation:
PIV of F.W.bridge R is 2Vm. Where as for a F.W.R with center tapped config
is Vm
4.The troubleshooting process for a typical dc power supply contains
four steps.
a)
True
b)
False
Answer: Option B
5.The number of electrons in a stable atom is the same as the
number of protons in its nucleus.
a)
True
b)
False
Answer: Option A
Explanation:
The atom becomes stable when it has no free electrons or it may bond with
another atom. In a stable atom number of electrons is equal to the no of
protons.
6.A rectifying diode can change ac voltage to dc voltage.
a)
True
b)
False
Answer: Option A
7.The barrier potential is the small difference of potential created by
positive and negative ions on either side of the depletion region.
a)
True
b)
False
Answer: Option A
8.Dark current is a small reverse current that flows in a photodiode
that is receiving no light.
a)
True
b)
False
Answer: Option A
9.One of the advantages of using transformer coupling in a halfwave rectifier is that it allows the ac source to be directly connected
to the load.
a)
True
b)
False
Answer: Option B
Explanation:
Transformer coupling helps in step up and step down of voltage.
10.A zener diode can be used to provide voltage regulation in a
power supply.
a)
True
b)
False
Answer: Option A
11.The positive lead of a diode is the cathode.
a)
True
b)
False
Answer: Option B
12.It is not possible to use a half-wave rectifier circuit without a
transformer.
a)
True
b)
False
Answer: Option B
Explanation:
You can rectify any AC voltage range using a single diode of desired power
rating.
13.Electrons in the conduction band are the only ones that are
included in the electron current flow.
a)
True
b)
False
Answer: Option A
Explanation:
Initially the conduction band is empty and valence band is completely filled.
When electrons in valence band moves to conduction band due to flow of
electrons conduction takes place.
14.The forward biased characteristics of a zener diode are the same
as those of a diode.
a)
True
b)
False
Answer: Option A
15.Breakdown voltage and peak inverse voltage are the same.
a)
True
b)
False
Answer: Option A
Explanation:
As far as I know, the PIV of a diode (in a rectifier) represents the maximum
voltage that appears across it. It doesn't mean that the diode will be
damaged if a higher voltage is applied across it.
16.An LED can be tested with an ohmmeter.
a)
True
b)
False
Answer: Option B
Explanation:
I think some analog tester can be used as a tester for LED since it has a
supply of 2-1.5V battery that make it 3volts enough to supply LED to light.
17.Reverse biasing a pn junction allows the flow of majority current.
a)
True
b)
False
Answer: Option B
18.A zener diode can be tested with an ohmmeter.
a)
True
b)
False
Answer: Option B
19.A diode can be tested with an ohmmeter.
a)
True
b)
False
Answer: Option A
20.A zener diode has a larger breakdown voltage than a diode.
a)
True
b)
False
Answer: Option B
21.The diode's characteristic curve shows that current increases
when voltage increases.
a)
True
b)
False
Answer: Option A
22.If a bridge rectifier is used, it is not necessary to use a
transformer.
a)
True
b)
False
Answer: Option A
23.Doping semiconductive material is the process of putting a small
amount of pentavalent or trivalent atoms in with tetravalent atoms.
a)
True
b)
False
Answer: Option A
24.A common problem with rectifiers is open diodes.
a)
True
b)
False
Answer: Option A
Fill in the blanks
1.
A ___ is created when an electron moves from the valence band to
the conduction band.
a)
Hole
b)
Gap
c)
Vacancy
d)
Blank
Answer: Option A
2.The average value of the half-wave rectified output voltage is
approximately __________ of Vp.
a)
31.8%
b)
63.6%
c)
70.7%
d)
100%
Answer: Option A
3.Typically the forward voltage on an LED is between _______ and
________.
a)
1.5 V, 3.7 V
b)
0.7 V, 1.1 V
c)
1 V, 3 V
d)
1 V, 6 V
Answer: Option C
4.A two-diode rectifier will not operate without a _________.
a)
Center-tapped transformer
b)
Voltage regulator
c)
Capacitive filter
d)
Phase-inverting transformer
Answer: Option A
e)
5.
The name of the circuit in the given circuit is the ___.
Half-wave rectifier
Center-tapped full-wave rectifier
Full-wave bridge rectifier
The four diodes are connected in bridge form so it is commonly
called as bridge rectifier (To improve efficiency)
6.The small amount of ac signal present on the output of a filtering
network for a dc power supply is known as ________.
a) Pulsating dc
b) Trickle
c) Ripple
d) Waffle
Explanation:
Ripple is defined as the ac component present in the rectified DC output
Rectifier does not converted in purely DC, so ripples are present there.
7.The peak output voltage from the circuit in the given circuit equals
___.
a) 3 V
b) 3.7 V
c) 2.3 V
d) 0 V
Answer: Option C
Explanation:
In semiconductor diode the barrier potential is 0.7 for silicon and 0.3 for
zermanium
8.An electron can move to another atom's orbit only while in the
_______.
a) Valence band
b) Conduction band
c) Orbit nearest the nucleus
d) Covalent band
Answer: Option B
9.The average value of the output voltage from the circuit in the
given circuit equals ___.
a) 5.48 V
b) 2.74 V
c) 0 V
d) 6.37 V
Answer: Option A
Explanation:
N2/N1=V2/V1 ==> 1/16=V2/160 ==> V2=10 VOLTS.
OUTPUT OF BRIDGE RECTIFIER IS 0.637V==> 0.637*10=6.37volts
10.Atoms in a silicon crystal are held together by ___ bonds.
a) Crystal
b) Chemical
c) Electrical
d) Covalent
Answer: Option D
Explanation:
Covalent is a mutual bond.
11.Special diodes designed to conduct in the reverse direction are
called _______________ diodes.
a) Zener
b) Varactor
c) LED
d) Switching
Answer: Option A
Explanation:
It is operated only reverse bias otherwise it will be acts as a common diode.
12.___ occurs when a pn junction is first formed.
a) Recombination
b) Covalent bonding
c) Crystallization
d) Breakdown
Answer: Option A
13.Connecting a capacitor filter to the circuit in the given circuit
will___.
a) Produce a nearly-constant dc voltage
b) Reduce the output voltage
c) Increase the ripple voltage
d) Lower the surge current
Answer: Option A
Explanation:
At the output we want pure DC voltage so by using capacitor filter it makes
potential difference and suppress unwanted interference & produce constant
DC voltage.
14.
The peak inverse voltage (PIV) for the diode in the give circuit
equals ___.
a) 3 V
b) 2.3 V
c) 0 V
d) 6 V
Answer: Option A
Explanation:
The peak inverse voltage is the maximum voltage the diode hold when it is
reverse bias. So, maximum voltage there is 3V which drops across the diode
during negative half cycle.
15.A pure semiconductor material ___ very well.
a) Conducts
b) Insulates
c) Conducts and insulates
d) Neither conducts nor insulates
Answer: Option D
Explanation:
For semi conductor to conduct, doping process is required i.e. Adding
impurities.
16.The small amount of ac signal present on the output of a filtering
network for a dc power supply is known as ________.
a) Pulsating dc
b) Trickle
c) Ripple
d) Waffle
Answer: Option C