Diodes and Transistors

1. A pure semiconductor is often referred to as a(n)

A. Extrinsic semiconductor

B. Intrinsic semiconductor

C. Doped semiconductor

D. None of the choices

2. An n -type semiconductor is a semiconductor that has been doped with

A. Trivalent impurity atoms

B. Impurity atoms whose electron valence is +4

C. Pentavalent impurity atoms

D. None of the choices

3. For a silicon diode, the barrier potential is approximately

A. 0.7 V

B. 0.3 V

C. 2.0 V

D. 6.8 V

4. In a p-type semiconductor, the majority current carriers are

A. Free electrons

B. Valence electrons

C. protons

D. holes

5. To forward-bias a diode,

A. The anode voltage must be positive with respect to its cathode

B. The anode voltage must be negative with respect to its cathode

C. The cathode voltage must be positive with respect to its anode

D. either “the anode voltage must be positive with respect to its cathode” or “the anode voltage must be negative with respect to its cathode”

6. A reverse-biased diode acts like a(n)

A. Closed switch

B. Open switch

C. Small resistance

D. None of the above

7. The sharing of valence electrons in a silicon crystal is called

A. doping

B. The avalanche effect

C. Covalent bonding

D. coupling

8. When used as a voltage regulator, a Zener diode is normally

A. forward-biased

B. reverse-biased

C. Not biased

D. None of the above

9. In an n -type semiconductor, the minority current carriers are

A. Free electrons

B. protons

C. Valence electrons

D. holes

10. A p -type semiconductor is a semiconductor doped with

A. Trivalent impurity atoms

B. Impurity atoms whose electron valence is +4

C. Pentavalent impurity atoms

D. None of the above

11. To a first approximation, a forward-biased diode is treated like a(n)

A. Open switch with infinite resistance

B. Closed switch with a voltage drop of 0 V

C. Closed switch in series with a battery voltage of 0.7 V

D. Closed switch in series with a small resistance and a battery

12. A 12-V Zener diode has a 1-W power rating. What is the maximum-rated Zener current?

A. 120 mA

B. 83.3 mA

C. 46.1 mA

D. 1 A

13. In a loaded Zener regulator, the series resistor has a current, IS, of 120 mA. If the load current, IL, is 45 mA, how much is the Zener current, IZ?

A. 45 mA

B. 165 mA

C. 75 mA

D. It cannot be determined

14. The approximate voltage drop across a forward- biased LED is

A. 0.3 V

B. 0.7 V

C. 5.6 V

D. 2.0 V

15. The output from an unfiltered half-wave or full- wave rectifier is a

A. Pulsating dc voltage

B. Steady dc voltage

C. Smooth dc voltage

D. None of the choices

16. A diode is a

A. Unidirectional device

B. Linear device

C. Nonlinear device

D. both “unidirectional device” and “nonlinear device”

17. What is the approximate dc output voltage from a filtered bridge rectifier whose peak output voltage is 30 V?

A. 19.1 V

B. 9.5 V

C. 30 V

D. None of the choices

18. At room temperature the current in an intrinsic semiconductor is due to

A. holes

B. electrons

C. ions

D. Holes and electrons

19. The most commonly used semiconductor material is

A. silicon

B. germanium

C. Mixture of silicon and germanium

D. None of the above

20. In which of these is reverse recovery time nearly zero?

A. Zener diode

B. Tunnel diode

C. Schottky diode

D. PIN diode

21. A transistor has a current gain of 0.99 in the CB mode. Its current gain in the CC mode is

A. 100

B. 99

C. 1.01

D. 0.99

22. In p-n-p transistor the current IE has two components, IEp due to injection of holes from p- region to n-region and IE due to injection of electrons from n-region to p-region. Then

A. IEp and IEn are almost equal

B. IEp >> IEn

C. IEn >> IEp

D. either “IEp and IEn are almost equal” or “IEn >> IEp”

23. In an n channel JFET, the gate is

A. N type

B. P type

C. Either n or p

D. Partially n & partially p

24. The amount of photoelectric emission current depends on

A. Frequency of incident radiation

B. Intensity of incident radiation

C. Both frequency and intensity of incident radiation

D. None of the above

25. Assertion (A): A p-n junction has high resistance in reverse direction.

Reason (R): When a reverse bias is applied to p-n junction, the width of depletion layer increases.

A. Both A and R are true and R is correct explanation of A

B. Both A and R are true but R is not a correct explanation of A

C. A is true but R is false

D. A is false but R is true

26. In the circuit of figure the function of resistor R and diode D are

A. To limit the current and to protect LED against over voltage

B. To limit the voltage and to protect LED against over current

C. To limit the current and protect LED against reverse breakdown voltage.

D. None of the above.

27. At very high temperatures the extrinsic semiconductors become intrinsic because

A. Drive in diffusion of dopants and carriers

B. Band to band transition dominants over impurity ionization

C. Impurity ionization dominants over band to band transition

D. Band to band transition is balanced by impurity ionization

28. When a voltage is applied to a semiconductor crystal then the free electrons will flow.

A. Towards positive terminal

B. Towards negative terminal

C. Either towards positive terminal or negative terminal

D. Towards positive terminal for 1μs and towards negative terminal for next 1μs

29. In a p type material the Fermi level is 0.3 eV above valence band. The concentration of acceptor atoms is increased. The new position of Fermi level is likely to be

A. 0.5 eV above valence band

B. 0.28 eV above valence band

C. 0.1 eV above valence band

D. Below the valence band

30. An LED has a rating of 2V and 10mA. It is used along with 6V battery. The range of series resistance is

A. 0 to 200 Ω

B. 200 - 400 Ω

C. 200 Ω and above

D. 400 Ω and above

31. The number of doped regions in PIN diode is

A. 1

B. 2

C. 3

D. 1 or 2

32. A transistor has two p-n junctions. The batteries should be connected such that

A. Both junctions are forward biased

B. Both junctions are reverse biased

C. One junction is forward biased and the other is reverse biased

D. None of the above

33. A silicon (PN) junction at a temperature of 20°C has a reverse saturation current of 10pA. The reverse saturation current at 40°C for the same bias is approximately.

A. 30 pA

B. 40 pA

C. 50 pA

D. 60 pA

34. In a bipolar transistor the barrier potential

A. 0

B. A total of 0.7 V

C. 0.7 V across each depletion layer

D. 0.35 V

35. Recombination produces new electron-hole pairs

A. True

B. False

C. Maybe

D. Depends on the material

36. Which transistor region is very thin and lightly doped?

A. The emitter region

B. The collector region

C. The anode region

D. The base region

37. Which region in a transistor is the most heavily doped?

A. The emitter region

B. The collector region

C. The gate region

D. The base region

38. In a transistor, which is the largest of all the doped regions?

A. The emitter region

B. The collector region

C. The gate region

D. The base region

39. For a transistor to function as an amplifier,

A. Both the EB and CB junctions must be forward- biased

B. Both the EB and CB junctions must be reverse- biased

C. the EB junction must be forward biased and the CB junction must be reverse-biased

D. the CB junction must be forward biased and the EB junction must be reverse-biased

40. For a typical transistor, which two currents are nearly the same?

A. IB and IE

B. IB and IC

C. IC and IE

D. None of the choices

41. In what operating region does the collector of a transistor act like a current source?

A. The active region

B. The saturation region

C. The cutoff region

D. The breakdown region

42. A transistor operating in the active region has a base current, IB , of 20uA. If βdc=250, how much is the collector current, IC ?

A. 50 mA

B. 5 mA

C. 12.5 mA

D. 80 uA

43. Which of the following biasing techniques produces the most unstable Q point?

A. Voltage divider bias

B. Emitter bias

C. Collector bias

D. Base bias

44. When the collector current in a transistor is zero, the transistor is

A. Cut off

Saturated

C. Operating in the breakdown region

D. either “saturated” or “operating in the breakdown region”

45. When a transistor is in saturation,

A. VCE = V CC

B. IC = 0A

C. VCE = 0 V

D. VCE = 1⁄2 V CC

46. Emitter bias with two power supplies provides a

A. Very unstable Q point

B. Very stable Q point

C. Large base voltage

D. None of the choices

47. The αdc of a transistor equals

A. IC / IE

B. IB / IC

C. IE / IC

D. IC / IB

48. For a transistor operating in the active region,

A. IC=βdc x IB

B. VCC has little or no effect on the value of IC

C. IC is controlled solely by VCC

D. both “IC=βdc x IB” and “VCC has little or no effect on the value of IC”

49. In a transistor amplifier, what happens to the collector voltage, VC, when the collector current, IC, increases?

A. VC increases

B. VC stays the same

C. VC decreases

D. It cannot be determined

50. With voltage divider bias, how much is the collector-emitter voltage, VCE, when the transistor is cut off?

A. VCE = 1⁄2 VCC

B. VCE = VCC

C. VCE =0 V

D. None of the choices

51. On the schematic symbol of a pnp transistor,

A. The arrow points out on the emitter lead

B. The arrow points out on the

C. The arrow points in on the base lead

D. The arrow points in on the emitter lead

52. What is the βdc of a transistor whose αdc is 0.996?

A. 249

B. 100

C. approximately 1

D. It cannot be determined

53. A bipolar junction transistor has

A. Only one p-n junction

B. Three p-n junctions

C. No p-n junctions

D. Two p-n junctions

54. The endpoints of a dc load line are labeled

A. ICQ and VCEQ

B. IC(sat) and VCE(off)

C. IC(off) and VCE(sat)

D. None of the choices

55. A JFET is a

A. Unipolar device

B. voltage-controlled device

C. Current controlled device

D. both “unipolar device” and “voltage-controlled device”

56. The drain and source leads may be interchanged when using a(n)

A. asymmetrical JFET

B. symmetrical JFET

C. D-type MOSFET

D. None of the choices

57. A JFET is a

A. normally ON device

B. normally OFF device

C. Bipolar device

D. current-controlled device

58. When a JFET is operating in the ohmic region,

A. ID is independent of VDS

B. ID is independent of VGS

C. ID increases in direct proportion to VDS

D. The drain acts like a current source

59. The value of drain to source voltage, V DS , at which the drain current, I D , levels off is called the

A. Cutoff voltage, VGS(off)

B. pinch-off voltage, VP

C. Breakdown voltage, VBR

D. Threshold voltage, VGS(th)

60. A JFET operates in the current source region when

A. VDS >VP

B. VDS < VP

C. VDS = 0 V

D. VGS = 0 V

61. A JFET parameter that describes how effective the gate-source voltage is in controlling the drain current is called its

A. gamma, γ

B. Beta, β

C. transconductance, gm

D. None of the choices

62. Which JFET amplifier is also known as a source follower?

A. The common-source amplifier

B. The common-gate amplifier

C. The common-channel amplifier

D. The common-drain amplifier

63. In which JFET amplifier are the ac input and output voltages 180 out of phase?

A. The common-gate amplifier

B. The common-source amplifier

C. The common-drain amplifier

D. The source follower

64. Which of the following JFET amplifiers has the lowest input impedance?

A. The common-gate amplifier

B. The common-source amplifier

C. The common-drain amplifier

D. The source follower

65. Which of the following JFET amplifiers has a high Zin, a low Zout, and a voltage gain less than one?

A. The common-gate amplifier

B. The common-source amplifier

C. The source follower

D. both “common-gate amplifier” and “common-source amplifier”

66. A depletion-type MOSFET is a

A. normally OFF device

B. normally ON device

C. current-controlled device

D. None of the choices

67. An enhancement-type MOSFET is a

A. normally OFF device

B. normally ON device

C. Low input impedance device

D. current-controlled device

68. For an enhancement-type MOSFET, the threshold voltage, VGS(th) , is the

A. Maximum allowable gate-source voltage before breakdown

B. gate-source voltage that produces a leveling off of ID

C. Minimum gate-source voltage that makes drain current flow

D. None of the choices

69. To avoid damaging MOSFETs during handling,

A. Always wear a grounded wrist strap.

B. Never apply an input signal when the dc power supply is OFF

C. Never insert or remove them from a circuit when the power is ON

D. All of the choices

70. Which of the following types of bias produces the most unstable Q point in a JFET amplifier?

A. Gate bias

B. current-source bias

C. Voltage divider bias

D. self-bias

71. When an n-channel JFET operates in the ohmic region,

A. rDS increases as VGS becomes less negative

B. rDS increases as VGS becomes more positive

C. rDS increases as V GS becomes more negative

D. rDS is independent of V GS

72. In a JFET amplifier with self-bias,

A. VG = 0V

B. VS = IDxRS

C. VGS = - IDxRS

D. All of the choices

73. For a depletion-type MOSFET with zero bias, the drain current, ID, equals

A. zero

B. IDSS

C. 1⁄2 IDSS

D. It cannot be determined

74. The input impedance of a MOSFET is

A. Higher than that of a JFET

B. Lower than that of a JFET

C. No different than that of a JFET

D. Approximately zero ohms

75. The shaded Y area is:

A. Active region

B. Saturation region

C. Cut-off region

D. Current region

76. The shaded X area is:

A. Active region

B. Saturation region

C. Cut-off region

D. Current region

77. The shaded Z area is:

A. Active region

B. Saturation region

C. Cut-off region

D. Current region

78. Determine IC at IB=30uA and VCE = 10V.

A. 6.6mA

B. 1mA

C. 3.4mA

D. 3mA

79. Determine the βdc at IB = 25uA and VCE = 7.5 V.

A. 100

B. 108

C. 200

D. 208

80. Determine the βac at IB = 25uA and VCE = 7.5 V.

A. 100

B. 108

C. 200

D. 208

81. Determine ID for a VGS of 3V and a Vp = 2V with an IDSS of 3mA.

A. 75mA

B. 750uA

C. 18.75mA

D. 187.5uA

A D-MOSFET has the following characteristics: IDSS = 10mA and VGS(off) = -4 V. Use this in the next 2 questions.

82. Calculate the drain current, ID, for VGS 2V.

A. 2.5mA

B. 3.7mA

C. 22.5mA

D. 37mA

83. Calculate the drain current, ID, for VGS -2V.

A. 2.5mA

B. 3.7mA

C. 22.5mA

D. 37mA

E-MOSFET circuit that has minimum values of ID(on) = 200 mA at VGS = 4 V and VGS(th) = 2 V. Se this in the next 2 questions.

84. Determine the k.

A. 0.05 mA/V^2

B. 0.3 mA/V^2

C. 50 mA/V^2

D. 30 mA/V^2

85. Determine ID at VGS = 3.13V.

A. 86.76 mA

B. 78.65 mA

C. 54.12 mA

D. 63.84 mA

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