Power Electronics Engineering Interview Questions set 3

What is a BJT (Bi Polar Junction Transistor)?

A bipolar junction transistor (BJT), unlike a thyristor-like device, is a two-junc­tion, self-controlled device where the collector current is under the control of the base drive cur­rent.

Why Darlington pair is used and what are its advantages and disadvantages?

The dc current gain of a power transistor is low and varies widely with collector current and temperature. The gain is increased to a high value in the Darlington connection,How­ever, the disadvantages are higher leakage current. higher conduction drop. and reduced switch­ing frequency.

How to control collector leakage current and enable base bias voltage?

The shunt resistances and diode in the base-emitter circuit help to reduce collector leakage current and establish base bias voltages.

What is avalanche breakdown (1st breakdown) and 2nd (second) breakdown in a BJT and how they destroy BJT?

Power transistors have an important property known as the second breakdown effect. This is in contrast to the avalanche breakdown effect of a junction, which is also known as first break­down effect. When the collector current is switched on by the base drive, it tends to crowd on the base-emitter junction periphery, thus constricting the collector current in a narrow area of the reverse-biased collector junction. This tends to create a hot spot and the junction fails by thermal runaway, which is known as second breakdown. The rise in junction temperature at the hot spot accentuates the current concentration owing to the negative temperature coefficient of the drop, and this regeneration effect causes collapse of the collector voltage, thus destroying the device.

What happens when inductive load is turned off in BJT circuitry?

when an inductive load is turned off the base-emitter junction becomes reverse-biased, the collector current tends to concentrate in a narrow area of the collec­tor junction. which causes the 2nd breakdown and BJT is destroyed after junction hotspot leading to thermal runaway of device.

What is a MOSFET, abbreviation and definition?

Unlike a BJT, a power MOSFET (metal-oxide semiconductor field-effect transistor) is a unipolar, majority carrier, "zero junction." voltage-controlled device.

Can you explain the working of a MOSFET?

If the gate voltage is positive and beyond a threshold value. an N-type conducting chan­nel will be induced that will permit current flow by majority carrier (electrons) between the drain and the source.

What is the major advantage/disadvantage of MOSFET over BJT?

An important property of a MOSFET is that it does not have the second breakdown problem of a BJT. If localized and potentially destructive heating occurs within the device. the positive temperature coefficient effect of resistance forces local current concentration to be uniformly distributed across the total area. The conduction loss of a MOSFET is large for higher voltage devices. its turn-on and turn-off switching times are extremely small, causing low switching loss. The device does not have the minority carrier storage delay problem associated with a bipolar device.

Please name a few applications of MOSFET?

MOSFETs are extremely popular in low-voltage, low-power. and high-frequency (hundreds of kHz) switching applications. Application examples include switching mode power supplies (SMPS), brushless dc motors (BLDMs). stepper motor drives. and solid-state dc relays.

Power Electronics Engineering Interview Questions set 2

What is GTO (Gate Turn Off Thyristor)?

A gate turn-off thyristor (GTO), as the name indicates, is basically a thyristor-type device that can be turned on by a small positive gate current pulse, but in addition, has the capability of being turned off by a negative gate current pulse.

How is the enhanced capability of a GTO obtained?

The turn-off capability of a GTO is due to the diversion of P-N-P collector current by the gate, thus breaking the P-N-P / N-P-N regenerative feedback effect.

What ratio of negative gate current is required to turn off a GTO?

The turn-off current gain of a GTO, defined as the ratio of anode current prior to turn-off to the negative gate current required for turn-off, is very low, typically 4 or 5. This means that a 6000 A GTO requires as high as –1500 A gate current pulse. However, the duration of the pulsed gate current and the cor­responding energy associated with it is small and can easily be supplied by low-voltage power MOSFETs.

What are Common applications of a GTO?

GTOs are used in motor drives, static VAR compensators (SVCs). and ac/dc power supplies with high power ratings. After large-power GTOs became available. they ousted the force-commutated, voltage-fed thyristor inverters.

What are series and shunt snubber and what is their application in power electronics?

The snubber consists of a turn-on component (R, L) called a series snubber and a turn-off component (R, C, and D), called a shunt snubber. This type of con­verter is typically used for a subway dc motor propulsion drive.

What do you mean by snubber loss?

The snubber loss may be substantial in a high-power and/or high-frequency converter. This, in turn, may reduce the converter's efficiency and put a burden on the cooling system. To combat this problem, various regenerative or energy recovery schemes have been proposed.

What are methods to cope with snubber loss

Passive energy recovery and the other is regenerative snubber.

What is Passive energy recovery method to overcome snubber loss?

When the GTO is turned off, the snubber capacitor„ charges to the full supply voltage, as usual. At the subsequent turn-on of the GTO, the stored energy is transferred to capacitor resonantly through the inductance and diode. When the GTO turns off again, the energy in capacitor is absorbed in the load and capacitor, charges again to voltage V.

What is regenerative snubber scheme to overcome snubber loss?

This scheme uses an auxiliary chopper. At GTO turn-off, the snubber capacitor, charges to supply voltage. At subsequent turn-on of the device, the energy is resonantly transferred to capacitor, as before. The energy in capacitor is then pumped to the source through a dc-to-dc boost converter.

What are common applications of regenerative snubbers and RC snubbers?

The idea of a regenerative snubber appears very attractive, but its application should be carefully weighed against the extra cost, loss, complexity, and equipment reliability. High-power GTO converters normally use regenerative snubbers. Otherwise, RC snubbers are commonly used.

Power Electronics Engineering Interview Questions set 1

 

Please name the most common silicon based semiconductor devices:

• Diode
• Thyristor or silicon-controlled rectifier (SCR)
• Triac
• Gate turn-off thyristor (GTO)
• Bipolar junction transistor (BJT or BPT)
• Power MOSFET
• Static induction transistor (SIT)
• Insulated gate bipolar transistor (IGBT)
• MOS-controlled thyristor (MCT)
• Integrated gate-commutated thyristor (IGCT)

 

What are Power Diodes and their usage in electrical and electronics engineering?

Power diodes provide uncontrolled rectification of power and are used in applications such as electroplating, anodizing, battery charging, welding, power supplies (dc and ac), and variable-frequency drives. They are also used in feedback and the freewheeling functions of converters and snubbers.

What is the basic structure of a power diode?

A typical power diode has P-I-N structure, that is, it is a P-N junction with a near-intrinsic semiconductor layer (I-layer) in the middle to sustain reverse voltage.

What is cause of Avalanche Breakdown, how it can be avoided?

In the reverse-biased condition, a small leakage current flows due to minority carriers, which gradually increase with voltage. If the reverse voltage exceeds a threshold value, called the breakdown voltage, the device goes through avalanche breakdown, which is when reverse current becomes large and the diode is destroyed by heating due to large power dissipation in the junction.

What is a fast-recovery diode?

In a fast-recovery diode, as the name indicates, the recovery time t and the recovery charge Q  are reduced by the minority carrier lifetime control that enhances the recombination process. However, the adverse effect is a higher conduction drop.

What is a Schottky diode, what are its advantages?

Schottky diode is basically a majority carrier diode and is formed by a metal-semiconductor junction. As a result, the diode has a lower conduction drop (typically 0.5 V) and faster switch­ing time, but the limitations are a lower blocking voltage (typically up to 200 V) and higher leak­age current.

What does the word “thyristor” means?

The term "thyristor" came from its gas tube equivalent, thyratron.

What devices belongs to Thyristor family?

That includes SCR, triac, GTO, MCT, and IGCT.

What is a thyristor and its construction and working?

Thyristors can be classified as standard, or slow phase-control-type and fast-switching, voltage-fed inverter-type. Basically. it is a three-junction P-N-P-N device, where P-N-P and N-P-N component transistors are connected in regenerative feedback mode. The device blocks voltage in both the forward and reverse direc­tions (symmetric blocking). When the anode is positive, the device can be triggered into conduc­tion by a short positive gate current pulse.

Does the gate of ordinary thyristor have ability to turn off?

Once the device is conducting, the gate loses its control to turn off the device.

In how many ways thyristor can be turned on?

Beside gate signal a thyristor can also turn on by excessive anode voltage, its rate of rise dv/dt, by a rise in junction temperature ( T_i), or by light shining on the junctions.

Please explain the turn on procedure of a thyristor using excess anode voltage?

If forward voltage is applied on the device, there will be a leakage current due to blocking of the middle junction. If the voltage exceeds a critical limit (breakover voltage), the device switches into con­duction. With increasing magnitude of I_G, the forward breakover voltage is reduced, and eventu­ally , the device behaves like a diode with the entire forward blocking region removed.

What is latching current and holding current in a thyristor?

The device will turn on successfully if a minimum current, called a latching current, is maintained. During conduction, if the gate current is zero and the anode current falls below a critical limit, called the holding current, the device reverts to the forward blocking state.

What are Triacs?

A triac has a complex multiple-junction structure, but functionally, it is an integration of a pair of phase-controlled thyristors connected in inverse-parallel on the same chip. The three-terminal device can be triggered into conduction in both positive and negative half-cycles of supply voltage by applying gate trigger pulses.

What are advantages and disadvantages of Triac over traditional thyristor equivalent circuit?

A triac is more economical than a pair of thyristors in anti-paral­lel and its control is simpler, but its integrated construction has some disadvantages. The gate current sensitivity of a triac is poorer and the turn-off time is longer due to the minority carrier storage effect.For the same reason, the reapplied dv/dt rating is lower, thus making it difficult to use with inductive load. A well-designed RC snubber is essential for a triac circuit.

What are common applications of a Triac?

Triacs are used in light dimming, heating control, appliance-type motor drives, and solid-state relays with typically 50/60 Hz supply frequency.

Electrical Engineering Objective Type MCQ’s Set 10

51. The time taken by the diode to operate in the reversed condition from forward conduction.

A. Maximum power time

B. Reverse recovery time

C. Lifetime

D. Time allocation

52. Approximately, the atomic weight of germanium is

A. 32

B. 28.09

C. 72.7

D. 16

53. Atomic weight of silicon at 300 K is

A. 28.09

B. 72.7

C. 5.32

D. 16

54. An LED and phototransistor is equivalent to a/an

A. Thermocouple

B. FET

C. Optocoupler

D. Regulator

55. Optocoupler is otherwise known as

A. Laser

B. Photodiodes

C. Optoisolator

D. Photoconductive cell

56. When the emitter junction is forward biased while the collector junction is reverse biased, the transistor is at ________ region.

A. Cut-off

B. Saturation

C. Active

D. Breakdown

57. When both emitter and collector junction are forward biased, the transistor is said to be at _________ region.

A. Active

B. Cut-off

C. Breakdown

D. Saturation

 

58. An equivalent circuit of a diode in which it is represented as a switch in series with a barrier potential.

A. First approximation

B. Second approximation

C. Third approximation

D. Fourth approximation

59. Which of the following is the equivalent circuit for a diode for third approximation?

A. A switch only

B. A switch in series with a battery in series with a resistance

C. A switch in series with battery

D. A switch in series with a resistance

60. A silicon crystal is a/an ___________ of a semiconductor if every atom in the crystal is a silicon atom.

A. Extrinsic

B. Intrinsic

C. P-type

D. N-type

61. With pnp voltage divider bias, you must use

A. Ground

B. Negative power supplies

C. Positive power supplies

D. Resistors

62. Two pn silicon diodes are connected in series opposing. A 5 V voltage is impressed upon them. Find the voltage across each junction at room temperature when nV_T= 0.052 V.

A. 0.236 V, 3.2 V

B. 4.764 V, 0.236 V

C. 0.036 V, 4.964 V

D. 3.21 V, 1.79 V

63. A half-wave signal has a period of

A. 16.7 ms

B. 8.3 ms

C. 16.7 µs

D. 8.3 µs

64. A full-wave signal has a period of

A. 16.7 µs

B. 8.3 µs

C. 8.3 ms

D. 16.7 ms

65. When doping increases, ________ of a semiconductor decreases.

A. Impurity

B. Conductivity

C. Bulk resistance

D. Minority carrier

66. Which of the following has the least noise level?

A. FET

B. BJT

C. Triode

D. Tetrode

67. Which of the following has the highest input impedance

A. FET

B. BJT

C. MOSFET

D. Crystal diode

68. The frequency of a half-wave signal is

A. Twice the line frequency

B. Equal to the line frequency

C. One-half of the line frequency

D. One-fourth the line frequency

69. For a full-wave rectifier, the output frequency

A. Equals one-half the input frequency

B. Equals the line frequency

C. Equals two times the input

D. Is three times the line frequency

70. The averaged dc voltage of a half wave rectifier circuit is _________ of the value of the peak input voltage.

A. 63.6%

B. 31.8%

C. 4.8%

D. 6.2%

71. The average dc voltage of a full wave rectifier circuit is __________ of the value of the peak input voltage.

A. 31.8%

B. 48.1%

C. 63.6%

D. 1%

72. Typical leakage current in a pn junction is in the order of

A. µA

B. mA

C. nA

D. pA

73. The resistance of a forward biased pn junction is in the order of

A. Ω

B. mΩ

C. µΩ

D. kΩ

74. The removal by electronic means of one extremity of an input waveform is called ________.

A. Filtering

B. Clamping

C. Amplifying

D. Clipping

 

75. Which of the choices below does not describe a clipper circuit?

A. Limiter

B. Amplitude selector

C. Slicer

D. Baseline stabilizer

 

76. The varactor diode is also called as

A. Voltage-variable capacitance

B. Varicap

C. Epicap

D. All of the above

 

77. What diode has no depletion layer

A. Varactor

B. Varistor

C. Schottky diode

D. Shockley diode

 

78. Varistors are used for line filtering to eliminate spikes and dips and is also called

A. Transient regulator

B. Transient limiter

C. Transient filter

D. Transient suppressor

 

 

79. Defined as random motion of holes and free electrons due to thermal agitation

A. Fission

B. Fusion

C. Diffusion

D. Ionization

80. The temperature coefficient of resistance of a semiconductor is

A. Positive

B. Negative

C. Zero

D. Infinity

81. A large signal amplifier which is biased so that collector current flow continuously during the complete electrical cycle of the signal as well as when no signal is present

A. Class A

B. Class B

C. Class AB

D. Class C

82. A large signal amplifier which is biased so that current is non zero for less than one-half cycle.

A. Class AB

B. Class C

C. Class A

D. Class B

83. A class ____ amplifier stage operates with a small forward bias of the transistor so that some collector current flows at all times

A. A

B. B

C. AB

D. C

84. What factor is shown on a data sheet that tells how much you have to reduce the power of a device?

A. Power factor

B. Derating factor

C. Reactive factor

D. Reduction factor

85. The time it takes to turn off a forward-biased diode is called the

A. Forward recovery time

B. Reverse recovery time

C. Recombination

D. Turn-off time

86. A heavily doped semiconductor has

A. High resistance

B. No effect on the semiconductor characteristics

C. More heat dissipation

D. Low resistance

 

87. Gallium arsenide, aluminum arsenide and gallium phosphide are classified as

A. Elementary semiconductor

B. Secondary semiconductor

C. Intrinsic material made by doping

D. Insulators

88. A lightly doped semiconductor has

A. Low resistance

B. High resistance

C. No effect on a semiconductor

D. More heat dissipated behaviors

89. The property or ability of a material to support charge flow or electron flow

A. Resistance

B. Conductance

C. Resistivity

D. Permeance

90. What is also known as photo diffusion effect?

A. Dember effect

B. Skin effect

C. Destriau effect

D. Night effect

91. An effect that occurs within the entire bulk of a semiconductor material rather than in a localized region or junction

A. Silicon effect

B. Dember effect

C. Bulk effect

D. Destriau effect

92. The creation voltage in a conductor or semiconductor by illumination of one surface

A. Dember effect

B. Skin effect

C. Destriau effect

D. Night effect

93. What device uses a material catwhisker as its anode and is classified as a hot-carrier diode?

A. PIN

B. Point-contact diode

C. Shockley diode

D. Crystal diode

94. What is the typical operating current of an LED?

A. 50 mA

B. 10 mA

C. 20 mA

D. 5 mA

95. At absolute zero temperature, a semiconductor behaves as a/an

A. Good conductor

B. Superconductor

C. Insulator

D. Variable resistor

96. Avalanche breakdown in a semiconductor takes place

A. When forward current exceeds a certain value

B. When potential barrier is reduced to zero

C. When reverse bias exceeds a certain value

D. When forward bias exceeds a certain value

97. A cold-cathode glow-discharge diode having a copper anode and a large cathode of sodium or other material.

A. Tunnel diode

B. BARITT diode

C. Anotron

D. READ diode

98. A microwave diode in which the carriers that transverse the drift region are generated by minority carrier injection from a forward-biased junction instead of being extracted from the plasma of an avalanche region.

A. IMPATT

B. TRAPAT

C. BARITT diode

D. Esaki diode

99. What electronic circuit converts AC to DC where the DC output peak value can be greater than the AC input peak value?

A. Voltage multiplier

B. Rectifier

C. Clamper

D. Clipper

100. Which of the item below does not mean a VARACTOR diode?

A. VOLTACAPS

B. VARICAPS

C. Voltage variable capacitors

D. Variable resistance diode

Electrical Engineering Objective Type MCQ’s Set9

1. How many electrons are there in the fourth orbit of a copper atom?

A. 1

B. 2

C. 3

D. 4

2. The maximum permissible number of electrons in the third orbit is

A. 18

B. 8

C. 32

D. 2

3. Varactor diodes are commonly used

A. As voltage controlled capacitance

B. As a constant current source

C. As voltage multiplier

D. As a constant voltage source

4. The reason why electrons are not pulled into the nucleus of an atom.

A. Because of the centrifugal or outward force created by their orbital motion.

B. Because of the force of attraction between them and the nucleus is weak.

C. Because they are not being attracted by the positive nucleus.

D. Because of the strong bonding between them that resists any force pulling them towards the nucleus.

5. The electrons in the largest orbit travel ________ than the electrons in the smaller orbits.

A. More slowly

B. Faster

C. In the same velocity

D. A little bit slower

6. A transistor configuration with the lowest current gain.

A. Common base

B. Common emitter

C. Common collector

D. Emitter-follower

7. A semiconductor in its purest form is called

A. Pure semiconductor

B. Doped semiconductor

C. Intrinsic semiconductor

D. Extrinsic semiconductor

8. Valence orbit is the other form for

A. Outer orbit

B. 3^rd orbit

C. 4^th orbit

D. 2^nd orbit

9. K shell means

A. First orbit

B. 2^nd orbit

C. 3^rd orbit

D. 4^th orbit

10. For either germanium or silicon diodes, the barrier potential decreases _______ for each Celsius degree rise.

A. 1 mV

B. 3 mV

C. 4 mV

D. 2 Mv

 

11. A diode modeling circuit which considers the threshold voltage, average resistance and switch as the diode’s equivalent circuit.

A. Ideal model

B. Simplified model

C. Piecewise linear model

D. Real model

12. There are two mechanisms by which holes and electrons move through a silicon crystal. They are

A. Covalent bond and recombination

B. Diffusion and drift

C. Free and charge particles

D. Forward and reverse bias

13. A semiconductor is an element with a valence of

A. Four

B. Eight

C. Two

D. One

14. What orbit controls the electrical property of the atom?

A. Valence orbit

B. First orbit

C. Fourth orbit

D. M shell

15. ________ is a substance that contains atoms with several bands of electrons but with only one valence electron.

A. Insulator

B. Conductor

C. Semiconductor

D. Resistor

16. Pure silicon crystal atoms contain how may valence electrons as a result of covalent bonding?

A. 1

B. 4

C. 8

D. 16

17. The peak inverse voltage of a full wave center tapped rectifier circuit is equal to _______ of the input signal.

A. Thrice the peak

B. Twice the peak

C. One half

D. One third

18. Diffusion or storage capacitance is the term used to refer to

A. The reverse bias capacitance of a diode

B. The forward bias capacitance of a diode

C. The breakdown capacitance of a zener diode

D. The effective capacitance of the rectifier

19. What is considered as the key electrical conductivity?

A. The number of electrons in the valence orbit

B. The number of protons in the nucleus

C. The number of neutrons in the nucleus

D. The number of protons plus the number of electrons in the atom

20. Each atom in the silicon crystal has how many electrons in its valence orbit?

A. 8

B. 32

C. 2

D. 4

21. Lifetime is the amount of time between the creation and disappearance of a/an

A. Free electron

B. Proton

C. Ion

D. Neutron

22. A silicon crystal is an intrinsic semiconductor

A. If every atom in the crystal is a silicon atom

B. If majority of the atoms in crystal is a silicon atom

C. If the crystal contains 14 silicon atoms

D. If the crystal is undoped

23. At room temperature, a silicon crystal acts approximately like a/an

A. Insulator

B. Semiconductor

C. Conductor

D. Superconductor

24. An extrinsic semiconductor is a

A. Doped semiconductor

B. Pure semiconductor

C. Good insulator

D. Good conductor

25. What is associated with random motion due to thermal agitation in the movement of holes and electrons in a silicon crystal?

A. Drift

B. Diffusion

C. Doping

D. Recombination

26. The peak inverse voltage of a half wave rectifier circuit is approximately equal to the ________ of the input signal.

A. Peak amplitude

B. Frequency

C. Voltage sinusoidal

D. Current

27. Silicon that has been doped with a trivalent impurity is called a/an

A. P-type semiconductor

B. N-type semiconductor

C. Intrinsic semiconductor

D. Extrinsic semiconductor

28. Silicon that has been doped with a pentavalent impurity is called a/an

A. N-type semiconductor

B. P-type semiconductor

C. Intrinsic semiconductor

D. Extrinsic semiconductor

29. What is another name for a pn crystal

A. Junction diode

B. PN junction

C. Diode

D. Lattice

30. An acceptor atom is also called

A. Pentavalent atom

B. Trivalent atom

C. Minority carrier

D. Majority carrier

31. Which is a donor atom?

A. Trivalent atom

B. Aluminum

C. Boron

D. Pentavalent atom

 

32. In an n-type semiconductor, free electrons are called

A. Minority carriers

B. Valence electrons

C. Majority carriers

D. Charge carriers

33. in an n-type semiconductor, holes are called

A. minority carriers

B. majority carriers

C. protons

D. charge carriers

34. What is the barrier potential of germanium at 25˚C

A. 0.7 V

B. 0.3 V

C. 0.5 V

D. 0.4 V

35. The barrier potential for a silicon diode at 25˚C is approximately

A. 0.4 V

B. 0.3 V

C. 0.7 V

D. 0.5 V

36. Each pair of positive and negative ions at the junction is called a/an

A. Anion

B. Positron

C. Cation

D. Dipole

 

37. When temperature increases, barrier potential ________

A. Remains the same

B. Decreases

C. Increases

D. Either increases or decreases depending on the semiconductor material used

38. Avalanche effects occurs at

A. Higher reverse voltages

B. Lower reverse voltages

C. Higher forward voltages

D. Lower forward voltages

39. The creation of free electrons through zener effect is also known as

A. Avalanche emission

B. Thermionic emission

C. Low-field emission

D. High-field emission

 

40. Zener effect only depends on the

A. High-speed minority carriers

B. High-speed majority carriers

C. Intensity of the electric field

D. Intensity of the magnetic field

41. What temperature is inside the diode, right at the junction of the p and n-type materials?

A. Junction temperature

B. Ambient temperature

C. Internal temperature

D. Absolute temperature

42. What is the input control parameter of a FET?

A. Gate voltage

B. Source voltage

C. Drain voltage

D. Gate current

43. One of the important diode parameters which gives the magnitude of current the diode candle without burning.

A. Reverse saturation current

B. Reverse current

C. Forward current

D. Forward breakdown current

44. The maximum reverse voltage that can be applied before current surges is called

A. Reverse recovery time

B. Maximum junction voltage

C. Forward voltage

D. Reverse breakdown voltage

 

45. What is the other name of Esaki diode?

A. Diac

B. Hot-carrier diode

C. Shockley diode

D. Tunnel diode

 

46. The most important application of Schottky diodes is in

A. Digital computers

B. Power supplies

C. Amplifier circuits

D. Voltage regulators

47. A diode is a nonlinear device because

A. It produces a nonlinear graph

B. Its current is not directly proportional to its voltage

C. It has a built-in barrier potential

D. It can rectify alternating current

48. The sum of the resistance of the p-region and the n-region is called

A. Junction resistance

B. Extrinsic resistance

C. Intrinsic resistance

D. Bulk resistance

 

49. What is the typical bulk resistance of rectifier diodes?

A. Less than 1Ω

B. Greater than1Ω

C. Equal to 1Ω

D. It depends on the doping level

50. The reverse bias diode capacitance is termed as

A. Transition region capacitance

B. Diffusion capacitance

C. Storage capacitance

D. Reverse capacitance

Electrical Engineering Objective Type MCQ's Set 8

251. A neon glow lamp used as a night light ionizes at approximately
A. 70 V
B. 80 V
C. 90 V
D. 100 V
252. What dielectric is generally employed by a variable capacitor?
A. Mica
B. Air
C. Electrolyte
D. Ceramic
253. A switch designed to have low capacitance between its terminal when open.
A. LOCAP switch
B. AntiLOCAP switch
C. Anticapacitance switch
D. Capacitance switch
254. A resistor wound with a wire doubled back on itself to reduce the inductance.
A. Bifilar resistor
B. Wire-wound resistor
C. Anti-inductive resistor
D. Bleeder resistor
255. What fusion of elements is without chemical action between them?A. Mixture
B. Compound
C. Alloy
D. Ionization
256. In calculating maximum instantaneous power ___ voltage or current is used.
A. Peak
B. Average
C. Rms
D. Instantaneous
257. The area of capacitor plates increases two times, then its capacitance
A. Increases two times
B. Increases four times
C. Decreases two times
D. Decreases four times
258. If the inductance is decreased, the impedance of the circuit containing a resistor a capacitor and an inductor connected in series to an ac source
A. Decreases
B. Increases
C. Decreases or increases
D. Decreases, increases or remains the same
259. When the movable plates of a gang capacitor completely overlap the fixed plates, the capacitance of the capacitor is
A. Halfway between maximum and minimum
B. Maximum
C. Minimum
D. Zero
260. In a circuit, a passive element is one whichA. Supplies energy
B. Receives energyC. Both supplies and receives energy
D. Attenuates signal
261. Rationalizing the denominator of a complex number means
A. Eliminating the j component in the denominator
B. Adding j component in the denominator
C. Eliminating the j component in the numerator
D. Adding j component in the numerator
262. When two complex conjugates are subtracted, the result is a
A. Quadrature component onlyB. Complex component
C. In-phase component
D. Real component
263. A coil of inductance L has an inductive reactance of X_L in an ac circuit in which the effective current is I. The coil is made from a superconducting material. The rate at which power is dissipated in the coil is
A. 0
B. I²X_L
C. IX_L
D. IX_L²
264. If the capacitance of mica capacitor is 5 times the capacitance of air capacitor, then the relative permittivity of mica is
A. 2.5
B. 5
C. 10
D. 25
265. The hot resistance of an incandescent lamp is about ___ times its cold resistance.
A. 10
B. 5
C. 50
D. 100
266. When the temperature of copper wire is increased its resistance is
A. Increased
B. Decreased
C. Constant
D. Zero
267. A trimmer is a variable capacitor in which capacitance is varied by changing the
A. Number of plates
B. Dielectric
C. Distance between plates
D. Plate area
268. The reason why electrical appliances are not connected in series.
A. Greater electrical power saving
B. Power loss is minimum
C. Appliances have different current ratings
D. All of the above
269. Form its definition, the unit of electric field, is the N/C and equivalent unit of is the
A. V(m)²
B. V(m)
C. V/m²
D. V/m
270. Which of the following is the peakiest?
A. Square wave
B. Sinusoidal wave
C. Triangular wave
D. Rectangular wave
271. Why are inductance and capacitance not relevant in a dc circuit?
A. Because it is a simple circuit
B. Because dc circuits require only resistance as load
C. Because they do not exist in a dc circuit
D. Because frequency of dc is zero
272. When capacitors are connected in parallel, the total capacitance is
A. Greater than the largest capacitor
B. Smaller than the largest capacitor
C. Smaller than the smallest capacitor
D. Greater than the smallest capacitor
273. When current and voltage arte in phase in an ac circuit, the ___ is equal to zero.
A. Resistance
B. Reactance
C. Inductance
D. Capacitance
274. Thevenin’s theorem is what form of an equivalent circuit?
A. Current
B. Voltage
C. Both current and voltage
D. Neither current nor voltage
275. Which of the following combination of length and cross-sectional area will give a certain volume of copper the least resistance?
A. 2L and1/2 A
B. Does not matter because the volume of copper remains the same
C. L and A
D. ½ L and 2 A
276. The ratio between the reactive power and the apparent power of an ac load is called
A. Quality factor
B. Power factor
C. Power ratio
D. Reactive power
277. What is the efficiency under the conditions of maximum power transfer?
A. 50 %
B. 100 %
C. 25 %
D. 75 %
278. The charging of a capacitor through a resistance follows what law?
A. Linear law
B. Hyperbolic law
C. Inverse-square law
D. Exponential law279. Norton’s theorem is what form of an ac equivalent circuit?
A. Voltage
B. Current
C. Both voltage and current
D. Neither voltage nor current
280. What is the total capacitance of 10 capacitors, each of 20 μF in series?
A. 200 μF
B. 2 μF
C. 100 μF
D. 0.5 μF
281. An inductive load always has a ___ power factor
A. Leading
B. Lagging
C. Zero
D. Unity
282. When resistance are connected in parallel, the total resistance is
A. Less than the smallest resistance in the connection
B. Greater than the smallest resistance in the connection
C. Between the smallest and greatest resistance in the connection
D. Increasing and decreasing depending upon the supply voltage
283. The arc across a switch when it open an RL circuit is a result of the
A. Large self-induced voltage across L
B. Long time constant
C. Low resistance of the open switch
D. Surge of resistance
284. What is a rotating vector whose projection can represent either current or voltage in an ac circuit?
A. Polar diagram
B. Scalar quantity
C. Velocity
D. Phasor
285. Which factor does not affect resistance?A. Length
B. Resistivity
C. Cross-sectional area
D. Mass
286. Which of the following capacitors are used only in dc circuits?
A. Mica
B. Ceramic
C. Mylar
D. Electrolytic
287. The maximum power transfer theorem is used in
A. Power system
B. Electronic system
C. Refrigeration
D. Air conditioning
288. In Norton’s theorem, the short circuit current is obtained by
A. Opening the load terminals
B. Shorting the load terminals
C. Opening the voltage source
D. Shorting the voltage source
289. For maximum power transfer, what is the relation between load resistance R_L and internal resistance R of the voltage source?
A. R_L = 2 r
B. R_L = 1.5 r
C. R_L = r
D. R_L = 3 r
290. A capacitor of 0.5 μF charged to 220 V is connected across an uncharged 0.5 μF capacitor. What is the voltage across each capacitor?
A. 220 V
B. 150 V
C. 110 V
D. 22 V
291. When capacitors are connected in series, the total capacitance is
A. Smaller than the smallest capacitor
B. Smaller than the largest capacitor
C. Greater than any of the capacitor
D. Greater than the largest capacitor
292. What theorem is generally used in the analysis of vacuum tubes?
A. Superposition theorem
B. Millman’s theorem
C. Thevenin’s theorem
D. Norton’s theorem
293. Another term of the quality factor of the resonant circuit.
A. Figure of merit
B. Figure of demerit
C. Noise factor
D. Noise figure
294. Which of the following represents the energy stored in a capacitor?
A. CV²/2
B. 2Q²/C
C. C²/V
D. CV
295. What theorem is usually used in the analysis of transistor circuit?A. Superposition theorem
B. Millman’s theorem
C. Thevenin’s theorem
D. Norton’s theorem
296. Which of the following capacitors has the highest cost per μF?
A. Plastic
B. Air
C. Mica
D. Electrolytic
297. Under the conditions of maximum power transfer, a voltage source is delivering a power of 15 W to the load. What is the power generated by the source?
A. 60 W
B. 30 W
C. 15 W
D. 4 W
298. Which of the following is neither a basic physical law nor deliverable from one?
A. Ohm’s law
B. Coulomb’s law
C. Kirchhoff’s first law
D. Kirchhoff’s second law
299. Another term for superconductor.
A. Generic conductor
B. Ultraconductor
C. Cryotron
D. Cryogenic conductor
300. A circuit whose parameters change with voltage or current.
A. Non-linear circuit
B. Linear circuit
C. Complex circuit
D. Passive circuit

• 
  

Electrical Engineering Objective Type MCQ's Set 7

201. The distance between the capacitor plates increases two times, then its capacitance
A. Increases two times
B. Increases four times
C. Decreases two times
D. Decreases four times
202. The ratio between the active power and the apparent power of a load in an ac circuit is called
A. Quality factor
B. Power factor
C. Power ratio
D. Power reactive
203. When the power factor of a circuit is zero,
A. Power absorbed is maximum
B. Power absorbed is minimum
C. Power absorbed is zero
D. The impedance is minimum
204. How many degrees of phase represents one full cycle?
A. 360
B. 180
C. 270
D. 90
205. Which of the following does not generally affect the value of a capacitor?
A. The dielectric material used
B. The surface area of the plates
C. The thickness of the dielectric
D. The voltage applied to the plate
206. What is the purpose of a load in an electric circuit?
A. To increase the circuit current
B. To decrease the circuit current
C. To utilize electrical energy
D. To make the circuit complete
207. The power factor of a certain circuit in which the voltage lags behind the current is 80 %. To increase the power to 100 %, it is necessary to add ___ to the circuit.
A. Inductance
B. Capacitance
C. Resistance
D. Impedance
208. Refers to the outward-curving distortion of the lines of force near the edges of two parallel metal plates that form a capacitor.
A. Skin effect
B. Night effect
C. Edge effect
D. Hall effect
209. If voltage across the plates of 2 F capacitor is increased by 4 V, then charge on the plates willA. Decrease by 2 C
B. Increase by 2 C
C. Decrease by 4 C
D. Increase by 4 C
210. What does a capacitor store?
A. Voltage
B. Charge
C. Current
D. Power
211. The mutual inductance between two coils is ___ the reluctance of magnetic path.
A. Directly proportional to
B. Inversely proportional to
C. Independent to
D. Equal to
212. The result of rust in electrical (wire) connection is
A. Inductance
B. Conductance
C. Impedance
D. Resistance
213. Which of the following is a disadvantage of a wire-wound resistor?
A. It has reactance in radio-frequency circuits
B. It cannot handle much power
C. It draws a large amount of current
D. It cannot handle high voltage
214. The resistance of an insulator ___ when its temperature is increased.
A. Decreases
B. Remains the same
C. Increases
D. Varies
215. The wavelength of an alternating waveform depends upon the ___ of the variation.
A. Period
B. Number
C. Frequency
D. Amplitude
216. Delta to wye or wye to delta transformation technique is applied to a ___ network.
A. One-terminal
B. Two-terminal
C. Three-terminal
D. Complex
217. For greater accuracy, the value of phase angle θ should be determined from
A. Cos θ
B. Tan θ
C. Sin θ
D. Sec θ
218. Inductive reactance applies only to sine waves because it
A. Increases with lower frequencies
B. Increases with lower inductance
C. Depends on the factor 2 π
D. Decreases with higher frequencies
219. What increases the resistance of wire at high frequencies?A. Temperature
B. Voltage
C. Skin effectD. Insulation
220. An inductor carries 2 A dc. If its inductance is 100 μH, then what is its inductive reactance?
A. Zero
B. 1.3 kΩ
C. 628 Ω
D. -628 Ω
221. Barium-strontium titanite dielectric material is also called
A. Ceramic
B. Polyster
C. Electrolytic
D. Bakelite
222. In the 5-band method of capacitor color coding, the first band indicates
A. Temperature coefficient
B. Tolerance
C. 1^st digit
D. Capacitance value
223. What is the most convenient way of achieving large capacitance?
A. By using multiplate construction
B. By using air as dielectric
C. By decreasing distance between plates
D. By using dielectric of low permittivity
224. A linear circuit is one whose parameters
A. Change with change in voltage
B. Change with change in current
C. Do not change with voltage and current
D. Change with change in voltage and current
225. For a linear circuit, ___ voltage or current is used to calculate average power.
A. Rms
B. Peak
C. Average
D. Instantaneous
226. When two coils of identical reactance are in parallel without mutual inductance, the reactance of the combination is ___ the reactance of each coil.
A. One half
B. Twice
C. Four times
D. One fourth
227. Which of the following is also known as anti-resonant circuit?
A. Parallel resonant circuit
B. Series resonant circuit
C. Tuned circuit
D. Tank circuit
228. In a complex number 5 + j 10, 10 is called ___ part.
A. Imaginary
B. Real
C. Conjugate
D. Integer
229. The presence of an electric current is made known byA. Electric shock
B. Effects produced
C. Magnetic shock
D. Flashing
230. The reciprocal of a complex number is
A. A complex number
B. A real number
C. An imaginary number
D. A whole number
231. Which of the following has negative temperature coefficient?
A. Carbon
B. Nickel
C. Brass
D. Constantan
232. Which of the following is a common material used in wire-wound resistors?
A. Manganin
B. Carbon
C. Bronze
D. German silver wire
233. If one resistance in a series connection is open, then
A. The current is zero in all the other resistances
B. The current is maximum in all the other resistances
C. The voltage is zero across the open resistance
D. The voltage is infinite across the open resistance
234. What determines the magnitude of electric current?
A. The rate at which electrons are produced
B. The type of material used
C. The current carrying capacity of the circuit
D. The rate at which electrons pass a given point
235. For a carbon composition resistor, typical resistance values range from
A. 2.7 Ω to 22 MΩ
B. 1000 Ω to 10000 Ω
C. 10 Ω to 10 MΩ
D. 2.7 Ω to 2.7 GΩ
236. A lead conductor has a resistance of 25 Ω at 0 ˚C. Determine its resistance at -30 ˚C
A. 22 Ω
B. 24 Ω
C. 12 Ω
D. 11 Ω
237. An impedance given by 90 -45˚ is a/an ___ impedance.A. Inductive
B. Conductive
C. Resistive
D. Capacitive
238. If a coil has a Q of 10, it means that
A. The energy stored in the magnetic field of the coil is 10 times the energy wasted in its resistance
B. The energy wasted in its resistance is 10 times the energy stored in the magnetic field of the coil
C. It is a low Q coil
D. It is a high Q coil
239. What is the rms value of a square wave?
A. Equals its peak value
B. Equals its peak-to-peak value
C. Peak divided by square root of two
D. Peak divided by pi
240. The rms value of a triangular or sawtooth waveform is ___ times its peak value.
A. 0.577
B. 0.500
C. 0.25
D. 0.707
241. In a multiple capacitor, the plate area is
A. Increased
B. The same
C. Decreased
D. Variable
242. What is the time constant for L of 240 mH in series with R of 20 Ω?
A. 12 ms
B. 4.8 s
C. 83.3 s
D. 12 s
243. In an ac circuit, the power dissipated as heat depends on
A. Impedance
B. Capacitive reactance
C. Resistance
D. Inductive reactance
244. Which of the following dielectric materials makes the lowest-capacitance capacitor?
A. Paper
B. Mica
C. Air
D. Electrolyte
245. In adding or subtracting phasor quantities, ___ form is the most convenient.A. Polar
B. RectangularC. Trigonometric
D. Exponential
246. In dividing or multiplying phasor quantities, ___ form is used.
A. Polar
B. Rectangular
C. Trigonometric
D. Exponential
247. The power factor of a circuit is equal to
A. RZ
B. X_C/Z
C. X_L/Z
D. R/Z
248. The capacitance of a capacitor is ___ relative permittivity.
A. Directly proportional to
B. Inversely proportional to
C. Equal to
D. Inversely proportional to the square of
249. If a multiplate capacitor has 10 plates, each of area 10 cm², then
A. 10 capacitors will be in parallel
B. 10 capacitors will be in series
C. 9 capacitors will be in parallel
D. 9 capacitors will be in series
250. Of the equivalent combination of units, which one is not equal to watt?
A. Ω²/V
B. AV
C. A²Ω
D. J/s

Electrical Engineering Objective Type MCQ’s Set 5

151. Metal tin becomes superconductor at approximately

A. 6 K

B. 3.7 K

C. 5 K

D. 4.7 K

152. In a complex resistance-reactance plane, X_L is represented

A. By an axis opposite the R axis

B. By an axis perpendicular to the X_C axis

C. By an axis opposite the X_C axis

D. By an axis parallel to the R axis

153. When the net reactance in a series coil-capacitor circuit is zero at frequency f, the nature of its reactance of frequency 2f is

A. Inductive

B. Capacitive

C. Resistive

D. Infinite

154. Which of the following is a way of decreasing mutual inductance?

A. Moving the coils closer

B. Moving the coils apart

C. Decreasing the number of turns of either coil

D. Increasing the number of turns of either coil

155. The charging of a capacitor through a resistance obeys

A. Exponential law

B. Logarithmic law

C. Linear law

D. Square law

156. The Q-factor of a parallel resonant circuit is also known as

A. Voltage magnification factor

B. Current magnification factor

C. Gain magnification factor

D. Resonance magnification factor

157. What is the specific resistance of a pure silicon?

A. 55 Ω-mm

B. 55 Ω-m

C. 55 Ω-cm

D. 55 kΩ-m

158. A capacitance of 0.05 μF equals

A. 0.05 x 10⁶ F

B. 0.05 x 10^-6 F

C. 0.05 x 10^-12 F

D. 0.05 x 10¹² F

159. A 5 μF capacitor charge to 5V has a stored charge equal to

A. 1 μc

B. 5 μc

C. 25 μC

D. 200 μc

160. The factor 0.707 for converting peak to rms applies only to

A. Square waves

B. Triangle waves

C. Sawtooth waves

D. Sine waves

161. When two in-phase sine waves that have identical frequency and amplitude are added together, then the result is a sine wave with ___ the amplitude of either.

A. Half

B. Twice

C. Four times

D. One-fourth

162. Liquids that are good conductors because of ionization are called

A. Electrolytic

B. Bases

C. Acid

D. Electrolytes

163. Tungsten filament of bulbs has a hot resistance higher than its cold resistance due to its temperature coefficient which is

A. Positive

B. Negative

C. Zero

D. Infinite

164. A term used to express the amount of electrical energy stored in electrostatic field.

A. Joules

B. Coulombs

C. Watts

D. Electron-volt

165. With double the number of turns by the same length and area, the inductance is

A. The same

B. Doubled

C. Quartered

D. Quadrupled

166. The temperature coefficient of resistance of electrolytes is

A. Negative

B. Positive

C. Zero

D. Infinite

167. What refers to the lowest voltage across any insulator that can cause current flow?

A. Conduction voltage

B. Critical voltage

C. Breakdown voltage

D. Voltage capacity

168. Capacitance increase with

A. Larger plate area and less distance between plates

B. Larger plate area and greater distance between plates

C. Smaller plate area and less distance between plates

D. Higher values of applied voltage

169. What is the resonant frequency of a circuit when L of 3 microhenrys and C of 40 picofarads are in series?

A. 14.5 kHz

B. 145 MHz

C. 14.5 MHz

D. 145 kHz

170. For a triangular and sawtooth waveform the rms voltage or current equals

A. 0.707 times peak value

B. 0.577 times peak value

C. 0.577 times average value

D. 0.707 times rms value

171. If two resistances of 9 Ω and 6 Ω are connected in parallel, the total resistance is

A. 54 Ω

B. 0.3 Ω

C. 15 Ω

D. 3.6 Ω

172. Refers specifically to steady state values of quantities in ac circuits which are complex numbers.

A. Domain

B. Scalar quantity

C. Vector quantity

D. Phasor quantity

173. A capacitor is used to

A. Block dc current

B. Pass dc current

C. Open voltage source

D. Short the voltage source

174. The usual load of a dc circuit is a/an

A. Resistor

B. Capacitor

C. Inductor

D. Both inductor and capacitor

175. The second strip of an electronic resistor color-code represents

A. The multiplier

B. The second digit of the value

C. The temperature

D. The tolerance

176. Which of the following is a preferred resistor value?

A. 520

B. 47

C. 43,000

D. 54,321

177. A three-by-three, series-parallel matrix of resistors, all having the same ohmic value, would have a net resistance of

A. One-third the value of a single resistor

B. Three times the value of a single resistor

C. The same value as a single resistor

D. Nine times the value of a single resistor

178. In an ac wave, 30 degrees of phase is ___ of a cycle.

A. ½

B. 1/12

C. 1/3

D. 1/30

179. What is the value of a carbon composition resistor with the following color code: Brown, white, orange, red

A. 190 Ω; 10 %

B. 19 kΩ; 2 %

C. 19 kΩ; 20 %

D. 1.9 kΩ; 2 %

180. The electric field strength between capacitor plates has a unit of

A. Volts per meter

B. Volts per mil

C. Amperes per meter

D. Amperes per mil

181. For multi-plate capacitor, capacitance is proportional to

A. Number of plates less one(n – 1)

B. Number of plates plus one(n + 1)

C. Number of plates less two(n - 2)

D. Number of plates (n)

182. A capacitor consists of two

A. Conductors only

B. Dielectric only

C. Conductors separated by a dielectric

D. Dielectric separated by a conductor

183. How many coulombs are delivered by a storage battery in 25 hours if it is supplying current at the rate of 3 A?

A. 2.592 x 10⁵ C

B. 2.592 x 10³ C

C. 2.592 x 10⁸ C

D. 2.592 x 10¹² C

184. When frequency of an ac wave decreases, the value of X_L in a coil

A. Approaches zero

B. Gets larger positively

C. Gets larger negatively

D. Stays constant

185. The temperature-resistance coefficient of pure gold is

A. 0.0034

B. 0.0037

C. 0.0038

D. 0.0039

186. The capacitor opposes any change in voltage across it by

A. Passing a voltage proportional to the rate of change of current

B. Acting as a short circuit at time equal to zero

C. Passing a current proportional to the rate of change of voltage

D. Acting as a short circuit at time equal to infinity

187. What is the most common non-sinusoidal waveform?

A. Square wave

B. Triangular wave

C. Trapezoidal wave

D. Sawtooth wave

188. Which of the following capacitors is suitable for dc filter circuits?

A. Mica

B. Ceramic

C. Paper

D. Electrolytic

189. A series RL circuit has R of 10 Ω and X_L of 5 Ω, its impedance in rectangular form is given by

A. 10 + j 5 Ω

B. 10 + j 10 Ω

C. 10 – j 5 Ω

D. 10 – j 10 Ω

190. What is the reciprocal of capacitance?

A. Reluctance

B. Susceptance

C. Elastance

D. Conductance

191. If the output resistance of a voltage source is 4 Ω, it internal resistance should be

A. 4 Ω

B. 8 Ω

C. 2 Ω

D. Infinite

192. The curve between current and frequency is termed as

A. Voltage curve

B. Gain curve

C. Power curve

D. Resonance curve

193. What is the total effective capacitance of two 0.25 μF capacitors connected in series?

A. 0.125 μF

B. 1.25 μF

C. 0.50 μF

D. 2.5 if

194. What can be used to estimate resonant frequency and to find reactance at any frequency for any value of capacitor or inductor?

A. Smith chart

B. Reactance chart

C. Impedance chart

D. Resonance chart

195. For a parallel AC circuit, ___ is used as a reference phasor.

A. Voltage

B. Power

C. Current

D. Resistance

196. For a series AC circuit, ___ is not used as a reference phasor.

A. Voltage

B. Impedance

C. Current

D. Conductance

197. If a certain circuit has a current that is lagging the voltage by 45˚, then it displays

A. Pure inductive reactance

B. Resistance and capacitance reactance

C. Resistance and inductive reactance

D. Pure capacitive reactance

198. What maximum voltage can be applied across the capacitor for very short period of time?

A. Working voltage

B. Surge voltage

C. Stray voltage

D. Peak voltage

199. What is expected when two 20 kΩ, 1 watt resistor in parallel are use instead of one 10 kΩ, 1 watt?

A. Provides higher current

B. Provides less power

C. Provides more power

D. Provides wider tolerance

200. Which of the following materials has the lowest dielectric strength?

A. Glass

B. Paper

C. Mica

D. Teflon