Unit IV Special purpose diodes and their applications Marks - 12

S. N. MSBTE Board Asked Questions Marks

1. Why is there a sudden increase in current in Zener diode?

a) Due to the rupture of ionic bonds
b) Due to rupture of covalent bonds

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c) Due to viscosity
d) Due to potential difference
Answer: b. Due to rupture of covalent bonds
1M
Explanation: The sudden increase in current in a Zener diode
is due to the rupture of the many covalent bonds present.
Therefore, the Zener diode should be connected in reverse
bias.

2. What is the semiconductor diode used as?

a) Oscillator
b) Amplifier
c) Rectifier
d) Modulator
1M
Answer: c. Rectifier
Explanation: Semiconductor diode can be used as a rectifier.
The function of a rectifier is that it converts an alternating
current into direct current by allowing the current to pass
 through in one direction.

3. What is rectification?
a) Process of conversion of ac into dc
b) Process of conversion of low ac into high ac
c) Process of conversion of dc into ac
d) Process of conversion of low dc into high dc

Answer: a. Process of conversion of ac into dc 1M

Explanation: Rectification is the process of conversion of
alternating current into direct current. The conversion first
powers to alternating current then use a transformer to
change the voltage, and finally rectifies power back to direct
current.

4. What is a Zener diode used as?

a) Oscillator
b) Regulator

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c) Rectifier
d) Filter

Answer: b. Regulator 1M
Explanation: Zener diode can be used as a voltage regulator.
They can also be used as shunt regulators to regulate the
voltage across small circuits. Zener diodes are always
operated in a reverse-biased condition.

5. Forward biasing of p-n junction offers infinite resistance.

a) True
b) False
Answer: b. False
Explanation: No, this is a false statement. Forward biasing of 1M
p-n junction offers low resistance. In the case of an ideal p-n
junction, the resistance offered is zero. So, forward biasing
does not offer any resistance.
6. When a junction diode is reverse biased, what causes
current across the junction?
a) Diffusion of charges
b) Nature of material
c) Drift of charges
d) Both drift and diffusion of charges
1M
Answer: c. Drift of charges
Explanation: The reverse current is mainly due to the drift of
charges. It is due to the carriers like holes and free electrons
passing through a square centimeter area that is
perpendicular to the direction of flow.

7. What can a p-n junction diode be used as?

a) Condenser
b) Regulator
c) Amplifier
d) Rectifier

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Answer: d. Rectifier
1M

Explanation: A junction diode can be used as a rectifier. The

rectifier converts alternating current into direct current.
During the positive half cycle, the diode is forward biased
and allows electric current through it.

8. In a PN junction with no external voltage, the electric field

between acceptor and donor ion is called a

a) Peak

b) Barrier

c) Threshold
1M
d) Path

Answer: (b) Barrier

Explanation:In p-n junction with no external voltage, the

electric field between the acceptor and the donor ions is
 called a barrier.

9. In a PN junction the potential barrier is due to the charges

on either side of the junction, these charges are

a) Majority carriers

b) Minority carriers

c) Both (a) and (b)

d) Fixed donor and accepter ions

1M
Answer: (d) Fixed donor and accepter ions

Explanation:The potential barrier created throughout the P-

N junction is due to the diffusion of electrons and holes, and
this potential barrier normally does not allow charging flow
through the junction.

The capacitance of a reverse-biased PN junction

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a) Increases as reverse bias is increased

b) Decreases as reverse bias is increased

c) Increases as reverse bias is decreased

10. d) Is significantly low

1M
Answer: (c) Increases as reverse bias is decreased

Explanation: When reverse bias decreases, the depletion

region width "d" decreases. As "d" increases, the capacitance
increases.

11. For a PN junction diode, the current in reverse bias maybe

a) Few milliamperes

b) Between 0.2 A and 15 A

c) Few amperes 1M

d) Few micro or nano amperes

Answer: (d) Few micro or nano amperes

 Explanation:n a reverse-biased diode, the current is very low,
typically in the nanoampere (nA) to picoampere (pA) range.
This is because the reverse bias causes the depletion region
to widen, making it difficult for current to flow across the
diode. The diode acts as an insulator in the reverse bias
condition.

12. When PN junction is in forward bias, by increasing the

battery voltage

a) Circuit resistance increases

b) Current through P_N junction increases

c) Current through P_N junction decreases

d) None of the above

1M
Answer: (b) Current through P_N junction increases

Explanation:When the voltage increases up to

around measurable current starts to flow through the diode

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in the forward direction. As the voltage moves a little above ,
the current through the diode rises rapidly.

13. When a PN junction is reverse biased

a) Holes and electrons tend to concentrate towards the junction

b) The barrier tends to break down

c) Holes and electrons tend to move away from the junction

d) None of these

Answer: (c) Holes and electrons tend to move away from the
junction 1M

Explanation:
junction Reverse bias applied to a p-n
diode raises the potential barrier because p-type material
connected to the negative terminal and pulls the holes away
from the junction. Similarly, n-type material connected to the
positive terminal and pulls the electrons
14. A PN junction

a) Has low resistance in forward as well as reverse directions

b) Has high resistance in forward as well as reverse directions

c) Conducts in the forward direction only

d) Conducts in the reverse direction only

Answer: (c) Conducts in the forward direction only

1M
Explanation:Diode is a combination of p-type and n-type
semiconductors. This combination creates a potential
barrier at the junction. Therefore, the external power source
must overcome the potential barrier to conduct. In the
forward bias, the diode conducts and in the reverse bias, it
will not conduct.

15. A PN junction is said to be forward-biased when

a) The positive terminal of the battery is connected to P-side

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and the negative side to the N-side

b) Junction is earthed

c) N-side is connected directly to the p-side

d) The positive terminal of the battery is connected to N-side

and the negative side to the P-side. 1M
Answer: (a) The positive terminal of the battery is connected
to P-side and the negative side to the N-side

Explanation:In forward biasing, the p-type is connected with

the positive terminal and the n-type is connected with
negative terminal of the battery.

16. PN Junction is also called ________.

a) diode
b) transistor 1M
c) triode
 d) inductor

Answer: a) Diode Explanation:Pn junctions are called diodes

because they
allow the flow of current in one direction and not in another,
they are two
and also terminals or distinct
because
electrodes, which are anode and cathode.

17. The P-type region of diode is called ________.

a) cathode
b) anode
c) grid

d) both a & b

Answer: b) anode
1M
Explanation:The anode is a positive terminal in a forward-

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biased p-n junction diode (that p-type is linked to
the
positive terminal and n-type is connected to the negative).
On this type of junction, the cathode terminal is negative. The
anode is a positively charged electrode or wire that charges
the p-n junction with holes.

18. The N-type of region of PN Junction diode is called

Cathode. True / False
Answer: True
Explanation:We
the N-type call the lead affixed to 1M
semiconductor the cathode. Therefore, the cathode is the
negative side of a diode.

19. When a diode is________bias then it shows the conventional

direction of current.

a) forward 1M

b) reverse
 Answer:a) forward

Explanation:The Conventional flow of current is from P side

to N side. As in a forward bias p-n junction the electrons
move from n side to p side, hence causing the conventional
current flow from P to N. *Conventional current flow is
always opposite to the direction of electrons flow.

20. How can we identify the positive and negative leads of a

diode?

a) colour coding
b) colour band
c) both a & b

d) none is correct 1M

Answer: c) both a & b

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Explanation:We can identify the positive and negative leads
of a diode by using colour coding colour band

21. PN Junction diode is a _________ device.

a) one way
b) two way
c) double way d) b

& c are correct

Answer: a) one way Explanation:A diode is often referred to 1M

as a one-way valve
because it allows current to flow in only one direction. When
a diode is forward-biased, it conducts current, but when it is
reverse-biased, it effectively blocks the flow of current.
22. The barrier potential of germanium is .3v. True / False
Answer: True
Explanation:Germanium (Ge) has a potential barrier of 0.3 1M
eV

23. The barrier potential of silicon is ________.

a) .3v
b) .7v
c) .5v

d) .4v 1M

Answer: b) 0.7 v

Explanation:Silicon (Si) has a potential barrier of 0.7 eV

24. The reverse saturation (Is) or maximum (Io) current during

reverse bias of a PN junction diode depends on _________.

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a) temperature
b) doping level
c) physical size of junction

d) all are correct

1M

Answer: d)all are correct Explanation:The reverse saturation

(Is) or maximum (Io)

current during reverse bias of a PN junction diode depends
on temperature, doping level, physical size of junction

25. How to protect a diode from increasing voltages of

breakdown level?

a) Filter capacitor 1M

b) Limiting resistor
 c) Zener diode

d) None is correct

Answer: b) Limiting resistor

Explanation: There is a series resistor connected to the

circuit in order to limit the current into the diode. It is
connected to the positive terminal of the d.c. It works in such
a way the reverse-biased can also work in breakdown
conditions.

26. Zener diodes are also known as

a) Voltage regulators
b) Forward bias diode
c) Breakdown diode
d) None of the mentioned

1M
Answer: c) Breakdown diode

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Explanation: Zener diodes are used as voltage regulators but
they aren’t called voltage regulators. They are called
breakdown diodes since they operate in breakdown region.

27. Which of the following is true about the resistance of a Zener

diode?
a) It has an incremental resistance
b) It has dynamic resistance
c) The value of the resistance is the inverse of the slope of the
i-v characteristics of the Zener diode
d) All of the mentioned
1M

Answer: d) All of the mentioned

Explanation: All of the statements are true for the resistance

of the zener diode.
28. Zener diode is designed to specifically work in which region
without getting damaged?
a) Active region
b) Breakdown region
c) Forward bias
d) Reverse bias

Answer: b) Breakdown region 1M

Explanation: The Zener diode is a specifically designed diode
to operate in the breakdown region without getting
damaged. Because of this characteristic, it can be used as a
constant-voltage device.

29. What is the level of doping in Zener Diode?

a) Lightly Doped

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b) Heavily Doped
c) Moderately Doped
d) No doping

Answer: b) Heavily Doped 1M

Explanation: A Zener diode is heavily doped so that the
breakdown voltage occurs at a lower voltage. If it were
lightly/moderately doped, it would breakdown at a
comparatively high voltage and, thus, would not be able to
serve its purpose.

30. When the reverse voltage across the Zener diode is increased
_____________
a) The value of saturation current increases
b) No effect 1M
c) The value of cut-off potential increases
d) The value of cut-off potential decreases
 Answer: c) The value of cut-off potential increases

Explanation: As the frequency of the incident radiation

increases, the kinetic energies of the emitted electron are
higher and therefore require more repulsive force to be
applied to stop them.
The value of saturation current increases, as the intensity of
the incident radiation, increases.
The value of cut-off potential decreases, as the frequency
decreases.

31. Zener Diode is mostly used as ____________

a) Half-wave rectifier
b) Full-wave rectifier
c) Voltage Regulator
d) LED

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Answer: c) Voltage Regulator
Explanation: The Zener diode, once in the breakdown region,
1M

keeps the voltage in the circuit to which it is connected as

constant. Thus it is widely used as a voltage regulator.

32. Which of the following is the correct symbol for the zener
diode?

a)
1M

b)

c)
 d)

Answer: d

Explanation: The following figure is the correct symbol for

the Zener diode.

The following figure is the symbol of a normal p-n junction

diode.

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33. In normal junctions, the breakdown is same as Zener
breakdown.
a) True
b) False

Answer: b) False 1M
Explanation: In normal p-n unction diodes, the breakdown
takes place by avalanche breakdown which is different than
the Zener breakdown. Zener diode is specifically made to
operate in that region.

34. The depletion region of the Zener diode is ____________

a) Thick
b) Normal
c) Very Thin 1M
d) Very thick
 Answer: c) Very Thin
Explanation: Zener diode is fabricated by heavily doping
both p- and n-sides of the junction, which results in an
extremely thin depletion region.

35. A light emitting diode is _________

a) Heavily doped
b) Lightly doped
c) Intrinsic semiconductor
d) Zener diode

1M
Answer: a) Heavily doped
Explanation: A light emitting diode, LED, is heavily doped. It
works under forward biased conditions. When the electrons
recombine with holes, the energy released in the form of
photons causes the production of light.

36. Which of the following materials can be used to produce

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infrared LED?
a) Si
b) GaAs
c) CdS
d) PbS
1M

Answer: b) GaAs
Explanation: GaAs has an energy band gap of 1.4 eV. It can be
used to produce infrared LED. Various other combinations
can be used to produce LED of different colors.

37. The reverse breakdown voltage of LED is very low.

a) True
b) False
Answer: a) True 1M
Explanation: The reverse breakdown voltages of LEDs are
very low, typically around 5 V. So, if access voltage is
 provided, they will get fused.

38. What should be the band gap of the semiconductors to be

used as LED?
a) 0.5 eV
b) 1 eV
c) 1.5 eV
d) 1.8 eV

1M
Answer: d) 1.8 eV

Explanation: Semiconductors with band gap close to 1.8 eV

are ideal materials for LED. They are made with
semiconductors like GaAs, GaAsP etc.

39. What should be the biasing of the LED?

a) Forward bias
b) Reverse bias

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c) Forward bias than Reverse bias
d) No biasing required

Answer: a) Forward bias

1M

Explanation: The LED works when the p-n junction is

forward biased i.e., the p- side is connected to the positive
terminal and n-side to the negative terminal.

40. Which of the following would have highest wavelength?

1M
 a) A
b) B
c) C
d) D

Answer: a) A

Explanation: In the I-V characteristic of an LED, as the

frequency increases, the voltage required to achieve the
same current increases. Hence A would have the highest
wavelength.

41. Increase in the forward current always increases the

intensity of an LED.
a) True
b) False

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Answer: b) False
Explanation: As the forward current is increased for an LED,
1M

the intensity of the light increases up to a certain maximum

value. After that, the intensity starts decreasing.

42. Which process of the Electron-hole pair is responsible for

emitting of light?
a) Generation
b) Movement
c) Recombination
d) Diffusion
1M

Answer: c) Recombination
Explanation: When the recombination of electrons with
holes takes place, the energy is released in the form of
photon. This photon is responsible for the emission of light.
43. Which of the following is not a characteristic of LED?
a) Fast action
b) High Warm-up time
c) Low operational voltage
d) Long life

1M
Answer: b) High Warm-up time
Explanation: The warm-up time required should be lower so
that the lighting action can take place faster. This is one of
the advantages LED have over incandescent lamps.

44. LEDs work on the principle of ______.

a) Electromagnetic induction

b) Conduction

c) Electroluminescence

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d) Induction
1M
Answer: c) Electroluminescence

Explanation: Electroluminescence is an electrical and optical

phenomenon where material emits light when electricity
flows through it.

45. State true or false: High warm-up time is needed for LEDs.

a) TRUE

b) FALSE

Answer: b) FALSE 1M

Explanation: little or no warm-up time is needed for light

emitting diodes.

46. Aluminium alloys are used to obtain _______ light.

1M
 a) Red

b) Orange

c) Yellow

d) All of the above

Answer: d) All of the above

Explanation: Aluminium alloys are used to obtain yellow,

orange, and red colour lights.

47. Why is there a sudden increase in current in Zener diode

a) Due to the rupture of ionic bonds

b) Due to rupture of covalent bonds
c) Due to viscosity
d) Due to potential difference
Answer: b) Due to rupture of covalent bonds
1M
Explanation: The sudden increase in current in a Zener diode

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is due to the rupture of the many covalent bonds present.
Therefore, the Zener diode should be connected in reverse
bias.

48. In a pure semiconductor crystal, if current flows due to

breakage of crystal bonds, then what is the semiconductor is
called?

a) Acceptor
b) Donor
c) Intrinsic semiconductor
d) Extrinsic semiconductor 1M
Answer: c) Intrinsic semiconductor

Explanation: Pure semiconductors are called intrinsic

semiconductors. The number of electrons in the conduction
band will be equal to the number of holes in the valence
band. Intrinsic semiconductors are also called undoped and
 i-type semiconductors

49. In a p-type semiconductor, germanium is doped with which

of the following?

a) Gallium
b) Copper
c) Phosphorous
d) Nitrogen
Answer: a) Gallium 1M
Explanation: Substances such as gallium, boron, and
aluminum are all trivalent atoms. These are called acceptor
impurities and they produce p-type semiconductors.
Therefore, germanium is doped with gallium in a p-type
semiconductor

50. What are the majority charge carriers in P-type

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semiconductors?

a) Electrons
b) Holes
c) Negative Ions
d) Positive Ions
Answer: b) Holes
1M
Explanation: Holes are the majority charge carriers in P-type
semiconductors. These holes are actually electron vacancies
that contain positive charge. The holes are responsible for
the conduction in p-type semiconductors.

5.1 Which of the following is operated in forward bias?

a) LED
b) Zener diode 1M

c) Photodiode
 d) Solar cell
Answer: a) LED

Explanation: A light-emitting diode (LED) converts electric

energy into light energy. A LED is a heavily doped p-n
junction which under forward bias emits spontaneous
radiation. The semiconductor used for the fabrication of
visible LEDs must at least have a bandgap of 1.8 eV.

52. In a shunt capacitor filter, the mechanism that helps the

removal of ripples is

a) The current passing through the capacitor

b) The property of capacitor to store electrical energy
c) The voltage variations produced by shunting the capacitor
d) Uniform charge flow through the rectifier
Answer: b) The property of capacitor to store electrical
energy
1M
Explanation: Filtering is frequently done by shunting the

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load with capacitor. It depends on the fact that a capacitor
stores energy when conducting and delivers energy during
non-conduction. Throughout this process, the ripples are
eliminated.

The charge (q) lost by the capacitor during the discharge

time for shunt capacitor filter.

a) IDC*T
b) IDC/T
c) IDC*2T
d) IDC/2T 1M

Answer: a) IDC*T

Explanation: The „T‟ is the total non-conducting time of

capacitor. The charge per unit time will give the current flow.
53. Which of the following are true about capacitor filter?

a) It is also called as capacitor output filter

b) It is electrolytic
c) It is connected in parallel to load
d) It helps in storing the magnetic energy
Answer: b) It is electrolytic 1M

Explanation: The rectifier may be full wave or half wave. The

capacitors are usually electrolytic even though they are large
in size

54. The rms ripple voltage (Vrms) of a shunt filter is

a) IDC/2√3
b) IDC2√3
c) IDC/√3
d) IDC√3

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Answer: a) IDC/2√3 1M

Explanation: The ripple waveform will be triangular in

nature. The rms value of this wave is independent of slopes
or lengths of straight lines. It depends only on the peak
value.

55. What is the effect of an inductor filter on a multi frequency

signal?

a) Dampens the AC signal

b) Dampens the DC signal
c) To reduce ripples
d) To change the current 1M
Answer: a) Dampens the AC signal

Explanation: Presence of inductor usually dampens the AC

signal. Due to self-induction induces opposing EMF or
changes in the current.
56. The inductor filter gives a smooth output because

a) It offers infinite resistance to ac components

b) It offers infinite resistance to dc components
c) Pulsating dc signal is allowed
d) The ac signal is amplified
Answer: a) It offers infinite resistance to ac components
1M
Explanation: The inductor does not allow the ac components
to pass through the filter. The main purpose of using an
inductor filter is to avoid the ripples. By using this property,
the inductor offers an infinite resistance to ac components
and gives a smooth output

57. Which of the following can be a source of supply in dc power

supplies?
a) Battery

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b) Dry cell
c) Full wave rectifier
d) All of the mentioned

1M

Answer: d) All of the mentioned

Explanation: Source of supply will be a battery, dry cell or
full wave rectifier etc.

58. Which of the application’s filters used for?

a) Reducing ripples
b) Increasing ripples
c) Increasing phase change
d) Increasing amplitude 1M

Answer: a) Reducing ripples

Explanation: Ripples are ac components and filters are used
 for eliminating ac components from a signal.

59. Which of the following represent a change of output voltage

when load current is increased?
a) Line regulation
b) Load regulation
c) Current regulation
d) Voltage regulation

1M
Answer: b) Load regulation

Explanation: Load regulation is the process of fractional

change of output voltage when load current is increased
from zero to maximum value.

60. Why zener diodes are provided in dc supply?

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a) For forward conduction
b) For reverse conduction
c) For reference voltage
d) For increasing amplitude

1M
Answer: c) For reference voltage

Explanation: Zener diodes in dc power supplies are used for

providing a reference voltage used for comparison.

61. Stability of output voltage is entirely depended on

______________
a) Stability of transformer
b) Stability of zener diode
c) Quality of wires 1M

d) Capacitor values
 Answer: b) Stability of zener diode
Explanation: Stability of zener diodes used is an important
factor in determining the stability of output voltage in dc
power supply.

62. Which of the following are not the standard value of Zener
diodes?
a) 5.1 V
b) 5.6 V
c) 5.8V
d) 6.2V
1M

Answer: c) 5.8V

Explanation: Standard values of zener voltages are 5.1V,

5.6V, 6.2V and 9.1V etc.

63 Which of the following can be used in series with a Zener

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diode so that combination has almost zero temperature
coefficient?
a) Diode
b) Resistor
c) Transistor
d) MOSFET

Answer: a) Diode
1M

Explanation: If a Zener diode of TC of about -2mV is

connected with a forward diode (which has a TC of about
+2mV) in series, the combination can be used to obtain a
very low (close to zero) TC.
64 _________ is used for critical loads where temporary
power failure can cause a great deal of inconvenience. a)
SMPS b) UPS c) MPS
d) RCCB

1M
Answer: b) UPS
Explanation: Uninterruptible Power Supply is used where
loads where temporary power failure can cause a great deal
of inconvenience.

65 __________ is used in the rotating type UPS system to supply the

mains.
a) DC motor
b) Self excited DC generator
c) Alternator

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d) Battery bank

1M
Answer: c) Alternator
Explanation: When the supply is gone, the diesel engine is
started, which runs the alternator and the alternator
supplies power to the mains. Non-rotating type UPS are not
used anymore.

66 Static UPS requires __________

a) only rectifier
b) only inverter
c) both inverter and rectifier
d) none of the mentioned
1M

Answer: c) both inverter and rectifier

Explanation: Rectifier to converter the dc from the battery to
 ac. Inverter to charge the battery from mains.

67 Usually __________ batteries are used in the UPS systems.

a) NC
b) Li-On
c) Lead acid
d) All of the mentioned

1M
Answer: c) Lead acid
Explanation: Lead acid batteries are cheaper and have
certain advantages over the other types. NC batteries would
however be the best, but are three to four times more
expensive than Lead Acid.

67 What is the expansion ofUPS?

a) Uninterrupted Power System

b) Uninterrupted Power Supply

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c) Uninterrupted Power Solution

d) Uninterrupted Power Section 1M

Answer: Uninterrupted Power Supply

Explanation: The full form of UPS is Uninterrupted Power

Supply

68 Which electrical / electronic devicerequires ups?

a) Air conditioner

b) Micro wave oven

c) Computer
1M
d) Television

Answer: Computer
 Explanation: Computer is required UPS for back up.

69 What is the number of capacitors and inductors used in a CLC

filter?
a) 1, 2 respectively
b) 2, 1 respectively
c) 1, 1 respectively
d) 2, 2 respectively

1M
Answer: b) 2, 1 respectively
Explanation: A very smooth output can be obtained by a filter
consisting of one inductor and two capacitors connected
across each other. They are arranged in the form of letter ‘pi’.
So, these are also called as pi filters.

70 Major part of the filtering is done by the first capacitor in a

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CLC filter because _________
a) The capacitor offers a very low reactance to the ripple
frequency
b) The capacitor offers a very high reactance to the ripple
frequency
c) The inductor offers a very low reactance to the ripple
frequency
d) The inductor offers a very high reactance to the ripple
frequency
1M

Answer: a) The capacitor offers a very low reactance to the

ripple frequency
Explanation: The CLC filters are used when high voltage and
low ripple frequency is needed than L section filters. The
capacitor in a CLC filter offers very low reactance to the
ripple frequency. So, maximum of the filtering is done by the
first capacitor across the L section part.
70 The inductor is placed in the L section filter because_________
a) It offers zero resistance to DC component
b) It offers infinite resistance to DC component
c) It bypasses the DC component
d) It bypasses the AC component

1M
Answer: a) It offers zero resistance to DC component
Explanation: The inductor offers high reactance to ac
component and zero resistance to dc component. So, it
blocks the ac component which cannot be bypassed by the
capacitors.

71 In practice the output from the diode rectifier has

a) AC component only
b) DC component only
c) AC + DC component
d) None of the mentioned

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Answer: c) AC + DC component
1M

Explanation: The output contents along with the DC

components the AC harmonics which does no useful work &
reduces the efficiency.

Choose the correct statement

78
a) The AC component in the output of rectifier does the
useful work
b) The AC component in the output of rectifier increases the
efficiency of the system
c) The AC component in the output of rectifier causes ohmic
losses 1M

d) The AC component in the output of rectifier does not affect

the operation

Answer: c) The AC component in the output of rectifier

 causes ohmic losses
Explanation: A rectifier is used to convert AC to DC. Lower
the AC (Non-DC) components in the output lower are the
ohmic losses.

An L filter is connected ________

79
a) in series
b) in parallel
c) in both series and parallel
d) none of the mentioned

1M
Answer: a) in series
Explanation: Inductor (L) has a very important property that
the current through it cannot change rapidly. We can make
use of this property by connecting it in series.

In case of an L filter connected with a rectifier in series with

80
the load, it offers ________ impedance to ac whereas _______

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resistance to dc respectively.
a) high, high
b) high, low
c) low, high
d) low, low
1M

Answer: b) ) high, low

Explanation: It offers high impedance to AC such as the AC

ripples do not pass through the load.

In case of a C filter, the AC is not allowed to pass to the load

81
by
a) offering it high impedance
b) offering it low impedance 1M
c) short circuiting the AC component
d) open circuiting the AC component
 Answer: c) short circuiting the AC component

Explanation: AC ripples are not allowed to pass, by S.C the AC

ripples as the C is always connected in parallel with the load.

A capacitor filter or C filter can be used in a rectifier by

82
connecting it
a) in parallel with the load
b) in series with the load
c) in parallel with the supply
d) in series with the supply
1M

Answer: a) in parallel with the load

Explanation: AC ripples are not allowed to pass, by S.C the AC
ripples as the C is always connected in parallel with the load.

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83
In a shunt capacitor filter, the mechanism that helps the
removal of ripples is_________
a) The current passing through the capacitor
b) The property of capacitor to store electrical energy
c) The voltage variations produced by shunting the capacitor
d) Uniform charge flow through the rectifier

Answer: b) The property of capacitor to store electrical

energy
1M
Explanation: Filtering is frequently done by shunting the
load with capacitor. It depends on the fact that a capacitor
stores energy when conducting and delivers energy during
non-conduction. Throughout this process, the ripples are
eliminated.
 The cut-in point of a capacitor filter is_________
84
a) The instant at which the conduction starts
b) The instant at which the conduction stops
c) The time after which the output is not filtered
d) The time during which the output is perfectly filtered

Answer: a) The instant at which the conduction starts 1M

Explanation: The capacitor charges when the diode is in ON
state and discharges during the OFF state of the diode. The
instant at which the conduction starts is called cut-in point.
The instant at which the conduction stops is called cut-out
point.

The rectifier current is a short duration pulses which cause

85
the diode to act as a_________
a) Voltage regulator
b) Mixer

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c) Switch
d) Oscillator

1M
Answer: c) Switch
Explanation: The diode permits charge to flow in capacitor
when the transformer voltage exceeds the capacitor voltage.
It disconnects the power source when the transformer
voltage falls below that of a capacitor.

The output waveform of CLC filter is superimposed by a

86
waveform referred to as_________
a) Square wave
b) Triangular wave
c) Saw tooth wave
1M
d) Sine wave
 Answer: c) Saw tooth wave
Explanation: Since the rectifier conducts current only in the
forward direction, any energy discharged by the capacitor
will flow into the load. This result in a DC voltage upon which
is superimposed a waveform referred to as a saw tooth wave.

A PN junction has a thickness of the order

87
a. 1 cm

b. 1 mm

c. 10-6 m

d. 10-12 cm

Answer: (c) 10-6 m

1M

Explanation: When P- type semiconductor is mixed with N -

type semiconductor, PN - junction is formed. There is very

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small region { which is in order of micro metre } . This region
is known as depletion region. so, the thickness of junction {
depletion region } is in order of 10 − 6 m

In the depletion region of an unbiased PN junction diode

88
there are

a. Only electrons

b. Only holes

c. Both electrons and holes

d. Only fixed ions

1M
Answer: (d) Only fixed ions

Explanation:Depletion region or depletion layer is a region

in a P-N junction diode where no mobile charge carriers are
present. Depletion layer acts like a barrier that opposes the
flow of electrons from n-side and holes from p-side.
 In Zener diode, the Zener breakdown takes place
89
a) Below 6 V

b) At 6 V

c) Above 6 V

d) None of the above

1M
Answer: a) Below 6 V

Explanation: Zener breakdown occurs where breakdown

voltage is below 6 V and Avalanche breakdown occurs for
other voltages.

A Zener diode when biased correctly

90
a) Never overheats

b) Has a constant voltage across it

c) Acts as a fixed resistance

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d) Has a constant current passing through it
1M

Answer: c) Has a constant voltage across it

Explanation: When biased correctly, the Zener diode has a

constant voltage across it.

Depletion region behaves as

91
a) Semiconductor

b) Insulator

c) Conductor

d) High resistance
1M
Answer: b) Insulator

Explanation: In the depletion region, an electric field exists

that quickly sweeps out electron-hole pairs that may be
thermally generated and reduces the equilibrium
 concentration of the charge carriers to exceedingly low
levels. Under these circumstances. This region, called the
depletion layer, behaves as an insulator.

The advantages of a pi-flter is_________

92
a) low output voltage

b) low PIV

c) low ripple factor

d) high voltage regulation

Answer: c) low ripple factor 1M

Explanation: Due to the involvement of 2 capacitors in

addition with one inductor it provides improved filtering
action. This leads to decrement in ripple factor. A low ripple
factor means the ratio of current due to AC ripples and direct
Current is low.

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93
The basic purpose of flter at the output of a rectifer is to

a) minimize variations in ac input signal

b) suppress harmonics in rectifed output

c) remove ripples from the rectifed output

d) stabilize dc output voltage

Answer: c) remove ripples from the rectifed output

1M
Explanation: Rectifier is an electrical device that converts AC
into DC by using one or more p-n junction diodes. But the
output of rectifiers is pulsating (means contains both AC
component and DC component). Hence, to remove all the AC
components we use filters.
 What is correct about the ripple factor of LC flter?
94
a) Increases with the load current
b) increases with the load resistance
c) remains constant with the load current
d) has the lowest value
Answer: c) remains constant with the load current 1M

Explanation: the ripple factor of LC flterremains constant

with the load current

Commercial power supplies have voltage regulation ________

95
A. of 10%
B. of 15%
C. of 25%
D. within 1%
1M

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answer: d) within 1%

Explanation: Commercial power supplies have voltage

regulation within 1%
In an unregulated power supply, if load current increases,
96 the output voltage __________

a) Remains the same

b) Decreases
c) Increases
d) None of the above

1M
answer: b)Decreases

Explanation: The DC voltage output is dependent on an

internal voltage reduction transformer and should be
matched as closely as possible to the current required by the
load. Typically the output voltage will decrease as the
current output to the load increases.
 Two similar 15 V Zeners are connected in series. What is the
97
regulated output voltage?

a) 15 V
b) 5 V
c) 30 V
d) 45 V
1M

Answer: c) 30 V

Explanation: As voltage and watt rating is more useful in real

applications. Now if we connect two 15 volts of Zener diodes
in series as above, then the total voltage will be 30 volts.
The voltage regulator output impedance is _______
98
a) Very small
b) Large
c) Infinite
d) None

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Answer: a) Very small

Explanation:A low impedance allows the source to deliver 1M

current without significant voltage drop, ensuring the

voltage remains stable even when connected to different
loads. This is important for many electrical and electronic
systems where a stable voltage is required for proper
operation.

A Zener diode utilises ………… characteristic for voltage

99
regulation

a) Forward
b) Reverse 1M

c) Both forward and reverse

 d) None of the above

Answer : b) Reverse

Explanation: A Zener diode utilises reverse characteristic for

voltage regulation

A Zener diode is used as a …………… voltage regulating device

a) Shunt
b) Series
100 c) Series-shunt

d) None of the above

1M
Answer : a) Shunt

Explanation: The Zener diode begins regulation operation

only when the input voltage (Vin ) is equal (or more than)

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Zener breakdown voltage (Vz). Otherwise, the diode remains
“Off-state”. Due to the parallel operation with load, Zener
diodes are referred to as shunt voltage regulators.
Which of the following is true about the temperature
coefficient or TC of the Zener diode?
a) For Zener voltage less than 5V, TC is negative
b) For Zener voltage around 5V, TC can be made zero
101
c) For higher values of Zener voltage, TC is positive
d) All of the mentioned

1M
Answer: d) All of the mentioned
Explanation: All of the mentioned are true for the TC of a
zener diode.
 Zener diodes can be effectively used in voltage regulator.
However, they are these days being replaced by more
efficient
a) Operational Amplifier
102 b) MOSFET
c) Integrated Circuits
d) None of the mentioned
1M

Answer: c) Integrated Circuits

Explanation: ICs have been widely adapted by the industries
over conventional zener diodes as their better replacements
for a voltage regulators.

Which of the following is true about the resistance of a Zener

diode?
103 a) It has an incremental resistance
b) It has dynamic resistance

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c) The value of the resistance is the inverse of the slope of the
i-v characteristics of the Zener diode
d) All of the mentioned

1M

Answer: d) All of the mentioned

Explanation: All of the statements are true for the resistance

of the zener diode.
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