## Electronics Engineering Multiple Choice Questions and Answers (MCQs) Part 2:

58. What is the typical value for the ratio of current in a p-n junction diode in the forward bias and that in the reverse bias?

(a) 1.
(b) 10.
(c) 100.
(d) 1000.

59. A p-n junction diode’s dynamic conductance is directly proportional to

(a) the applied voltage.
(b) the temperature.
(c) its current.
(d) the thermal voltage.

60. A p-n junction has a built-in potential of 0.8 V. The depletion layer width at a reverse bias of 1.2 V is 2 Î¼m. For a reverse bias of 7.2 V, the depletion layer width will be

(a) 4 Î¼m
(b) 4.9 Î¼m
(c) 8 Î¼m
(d) 12 Î¼m

61. The diffusion capacitance of a p-n junction diode

(a) increases exponentially with forward bias voltage.
(b) decreases exponentially with forward bias voltage.
(c) decreases linearly with forward bias voltage.
(d) increases linearly with forward bias voltage.

Answer : (a) increases exponentially with forward bias voltage.

62. In a step-graded p-n junction diode, what is the ratio of depletion-region penetration depths into p and n regions (if the ratio of acceptor to donor impurity atoms densities is 1 : 2) ?

(a) 2 : 1
(b) 4 : 1
(c) 1 : 2
(d) 1 : 4

Answer : (a) 2 : 1

63. A region of negative differential resistance is observed in the current voltage characteristics of a silicon PN junction if

(a) both the P-region and the N-region are heavily doped.
(b) the N-region is heavily doped compared to the P-region.
(c) the P-region is heavily doped compared to the N-region.
(d) an intrinsic silicon region is inserted between the P-region and N-region.

Answer : (a) both the P-region and the N-region are heavily doped.

64. A Zener diode, when used in voltage stabilization circuits, is biased in

(a) reverse bias region below the breakdown voltage.
(b) reverse breakdown region.
(c) forward bias region.
(d) forward bias constant current mode.

Answer : (b) reverse breakdown region.

65. The I-V characteristics of a tunnel diode exhibit?

(a) current-controlled negative resistance.
(b) voltage-controlled negative resistance.
(c) temperature-controlled positive resistance.
(d) current-controlled positive resistance.

Answer : (b) voltage-controlled negative resistance.

66. Consider the following statements pertaining to tunnel diodes :

1. Impurity concentration is high.
2. Carrier velocities are low.
3. They have current-controlled V-I characteristic.

Which of the statements given above is / are correct ?

(a) 1 only.
(b) 2 and 3 only.
(c) 1 and 3 only.
(d) 1 and 2 only.

67. Intermediate (I) layer of PIN-diode imparts which one of the following features to a pn junction diode ?

(a) High reverse blocking capability.
(b) High forward current rating.
(c) Inverting capability.
(d) Poor turn off performance.

Answer : (a) High reverse blocking capability.

68. Which of the following does not show nonlinear V-I characteristics?

(a) Schottky diode.
(b)Tunnel diode.
(c) Thermister, at a fixed temperature.
(d) p-n junction diode.

Answer : (c) Thermister, at a fixed temperature.

69. Ripple frequency of the output waveform of a full-wave rectifier when fed with a 50 Hz sine wave is

(a) 25 Hz
(b) 50 Hz
(c) 100 Hz
(d) 200 Hz

70. The function of bleeder resistor in a power supply is

(a) to ensure a minimum current drain in the circuit.
(b) to increase the output dc voltage.
(c) to increase the output current.
(d) same as that of a load resistor.

Answer : (a) to ensure a minimum current drain in the circuit.

71. If the input voltage to a voltage trippler has an rms value of 12 V, the dc output voltage is approximately

(a) 36 V
(b) 50.9 V
(c) 33.9 V
(d) 32.4 V

72. The emitter of a transistor is generally doped the heaviest because it

(a) has to dissipate maximum power.
(b) has to supply the charge carriers.
(c) is the first region of the transistor.
(d) must possess low resistance.

Answer : (b) has to supply the charge carriers.

73. An emitter in a bipolar junction transistor is doped much more heavily than the base as it increases the

(a) emitter efficiency.
(b) base transport factor.
(c) forward current gain.
(d) all the three given above.

Answer : (d) all the three given above.

74. The impurity commonly used for realizing the base region of a silicon n-p-n transistor is

(a) Gallium.
(b) Indium.
(c) Boron.
(d) Phosphorus.

75. For an npn bipolar transistor, what is the main stream of current in the base region ?

(a) Drift of holes.
(b) Diffusion of holes.
(c) Drift of electrons.
(d) Diffusion of electrons.

Answer : (b) Diffusion of holes.

76. The current ICBO flows in the

(d) none of these.

77. In a junction transistor, the collector cut-off current ‘ICBO‘ reduces considerably by doping the

(a) emitter with high level of impurity.
(b) emitter with low level of impurity.
(c) collector with high level of impurity.
(d) collector with low level of impurity.

Answer : (a) emitter with high level of impurity.

78. A BJT is said to be operating in the saturation region if

(a) both the junctions are reverse biased.
(b) base-emitter junction is reverse biased and base-collector junction is forward biased.
(c) base-emitter junction is forward biased and base-collector junction is reverse-biased.
(d) both the junctions are forward biased.

Answer : (d) both the junctions are forward biased.

79. When a bipolar junction transistor is operating in the saturation mode, which one of the following statements is TRUE about the state of its collector-base (CB) and the base-emitter (BE) junctions?

(a) The CB junction is forward biased and the BE junction is reverse biased.
(b) The CB junction is reverse biased and the BE junction is forward biased.
(c) Both the CB and BE junctions are forward biased.
(d) Both the CB and BE junctions are reverse biased.

Answer : (c) Both the CB and BE junctions are forward biased.

80. The dc current gain (Î²) of BJT is 50. Assuming that the emitter injection efficiency is 0.995, the base transport factor is

(a) 0.980
(b) 0.985
(c) 0.990
(d) 0.995

81. If Î±F and Î±R denote the forward and inverted mode current gains of a BJT, which one of the following is correct ?

(a) Î±FÂ = Î±R
(b) Î±F < Î±R
(c) Î±F â‰¥Â Î±R
(d) Î±F >> Î±R

Answer : (d) Î±F >> Î±R

82. In a bipolar transistor at room temperature, if the emitter current is doubled the voltage across its base-emitter junction

(a) doubles.
(b) halves.
(c) increases by about 20 mV.
(d) decreases by about 20 mV.

83. The Early Effect in a bipolar junction transistor is caused by

(a) fast turn-on.
(b) fast turn-off.
(c) large collector-base reverse bias.
(d) large emitter-base forward bias.

Answer : (c) large collector-base reverse bias.

84. The modulation of effective base width by collector voltage is known as Early Effect. Hence reverse collector voltage

(a) increases both alpha and beta.
(b) decreases both alpha and beta.
(c) increases alpha but decreases beta.
(d) decreases beta but increases alpha.

Answer : (c) increases alpha but decreases beta.

85. The output impedance of a BJT under common-collector configuration is

(a) low.
(b) high.
(c) medium.
(d) very high.

86. Consider the following circuit configurations:

1. Common emitter.
2. Common base.
3. Emitter follower.
4. Emitter follower using Darlington pair.

The correct sequence in increasing order of the input resistances of these configurations is

(a) 2, 1, 4, 3.
(b) 1, 2, 4, 3.
(c) 2, 1, 3, 4.
(d) 1, 2, 3, 4.

Answer : (c) 2, 1, 3, 4.

87. Which one of the following statements is not correct ?

(a) Reverse saturation current in a BJT approximately doubles for every 10Â°C rise in temperature.
(b) The reverse resistance of a junction diode increases with increase in temperature.
(c) Reverse saturation current of a silicon diode is much smaller than that of a germanium diode.
(d) The cut-in voltage of silicon diode is larger than that of germanium.

Answer : (b) The reverse resistance of a junction diode increases with increase in temperature.

88. For a transistor, turn-off time is:

(a) Sum of storage time and fall time.
(b) Maximum value of storage time.
(c) Maximum value of fall time.
(d) Sum of rise time and fall time.

Answer : (a) Sum of storage time and fall time.

89. Consider the following statements:

The basic purpose of bias stabilization in a transistor circuit is to

1. increase the voltage and current gain of the amplifier.
2. make the operating point of the transistor independent of temperature variation of the transistor.
3. make the operating point independent of the replacement of the same type, Ge or Si.

Which of the statements given above are correct ?

(a) 1 and 2 only.
(b) 2 and 3 only.
(c) 1 and 3 only.
(d) 1, 2 and 3.

Answer : (b) 2 and 3 only.

90. The emitter resistor RE is bypassed by a capacitor in order to

(a) stabilize the Q-point.
(b) cause thermal run away.
(c) increase the voltage gain.
(d) reduce the voltage gain.

Answer : (a) stabilize the Q-point.

91. Introducing a resistor in the emitter of a common amplifier stabilizes the dc operating point against variations in

(a) only the temperature.
(b) only the Î² of the transistor.
(c) both temperature and Î².
(d) none of the above.

Answer : (c) both temperature and Î².

92. If the emitter resistance in a common-emitter voltage amplifier is not bypassed, it will

(a) reduce both the voltage gain and the input impedance.
(b) reduce the voltage gain and increase the input impedance.
(c) increase the voltage gain and reduce the input impedance.
(d) increase both the voltage gain and the input impedance.

Answer : (b) reduce the voltage gain and increase the input impedance.

93. The biasing of an IC BJT is done by the following biasing scheme:

(a) Potential-divider biasing scheme.
(b) Fixed biasing scheme.
(c) Current mirror biasing scheme.
(d) Collector to base feedback biasing scheme.

Answer : (c) Current mirror biasing scheme.

94. The action of a JFET in its equivalent circuit can best be represented as a

(a) Current Controlled Current Source
(b) Current Controlled Voltage Source
(c) Voltage Controlled Voltage Source
(d) Voltage Controlled Current Source

Answer : (d) Voltage Controlled Current Source

95. Consider the following statements:

FETs when compared to BJTs have

1. high input impedance.
2. current flow due to majority carriers.
3. low input impedance.
4. current flow due to minority carriers.

Which of the statements given above are correct ?

(a) 1 and 4
(b) 2 and 3
(c) 3 and 4
(d) 1 and 2

Answer : (d) 1 and 2

96. A FET is a better chopper than a BJT because it has

(a) lower off-set voltage.
(b) higher series ON resistance.
(c) lower input current.
(d) higher input impedance.

Answer : (a) lower off-set voltage.

97. Thermal runaway is not encountered in FETs because

(a) IDS has a zero temperature coefficient.
(b) IDS has a negative temperature coefficient.
(c) IDS has a positive temperature coefficient.
(d) the mobility of the carriers increases with increase in temperature.

Answer : (a) IDS has a zero temperature coefficient.

98. In an MOS transistor, the gate source input impedance is

1. lower than the input impedance of a BJT.
2. higher than the input impedance of a BJT.
3. lower than the input impedance of a JFET.
4. higher than the input impedance of a JFET.

Select the correct answer using the codes given below:

(a) 1 alone.
(b) 2 and 3.
(c) 4 alone.
(d) 2 and 4.

Answer : (d) 2 and 4.

99. The lower turn off time of MOSFET when compared to BJT can be attributed to which one of the following ?

(a) Input impedance.
(b) Positive temperature coefficient.
(c) Absence of minority carriers.
(d) On-state resistance.

Answer : (c) Absence of minority carriers.

100. If fixed positive charges are present in the gate oxide of an n-channel enhancement type MOSFET, it will lead to

(a) a decrease in the threshold voltage.
(b) channel length modulation.
(c) an increase in substrate leakage current.
(d) an increase in accumulation capacitance.

Answer : (a) a decrease in the threshold voltage.

101. A CMOS amplifier when compared to an N-channel MOSFET, has the advantage of

(a) higher cut-off frequency.
(b) higher voltage gain.
(c) higher current gain.
(d) lower current drain from the power supply, thereby less dissipation.

Answer : (d) lower current drain from the power supply, thereby less dissipation.

102. Which of the following devices is used in the microprocessors?

(a) JFET.
(b) BJT.
(c) MOSFET.
(d) CMOS.

103. The voltage gain of a given common source JEFF amplifier depends on its

(a) input impedance.
(b) amplification factor.
(c) dynamic drain resistance.

104. An ideal amplifier

(a) has + ve feedback.
(b) gives uniform frequency response.
(c) has infinite voltage gain.
(d) responds only to signals at its input terminals.

Answer : (d) responds only to signals at its input terminals.

105. Consider the following statements:

To draw ac equivalent circuit of a transistor, all

1. dc sources are shorted.
2. ac sources are shorted.
3. dc sources are opened.
4. ac sources are connected to dc sources.

Which of the above statements is/are correct?

(a) 2 and 4.
(b) 1 and 2.
(c) 1 only.
(d) 3 and 4.