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Unit 4: Fundamentals of semiconductor devices - Practice Quiz

ECE131 — Basic Electrical And Electronics Engineering 60 Questions
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1 Which material is commonly used to manufacture semiconductor devices?

Introduction to semiconductor devices Easy
A. Copper
B. Aluminum
C. Iron
D. Silicon

2 What process adds impurities to a pure semiconductor to change its conductivity?

Introduction to semiconductor devices Easy
A. Magnetization
B. Doping
C. Rectification
D. Insulation

3 How is a PN junction diode connected for forward bias?

Working and operation of PN junction diode Easy
A. P-side to positive and N-side to negative
B. Both sides to the negative terminal
C. Both sides to the positive terminal
D. P-side to negative and N-side to positive

4 What happens to the depletion region of a PN junction diode during forward bias?

Working and operation of PN junction diode Easy
A. It becomes an insulator
B. It becomes wider
C. It remains unchanged
D. It becomes narrower

5 What is the approximate forward voltage drop of a conducting silicon diode?

Characteristics of PN junction diode Easy
A.
B.
C.
D.

6 In which bias condition does a PN junction diode normally carry only a very small leakage current?

Characteristics of PN junction diode Easy
A. Zero bias
B. Breakdown bias
C. Forward bias
D. Reverse bias

7 In which bias condition is a Zener diode normally operated for voltage regulation?

Working and operation of Zener diode Easy
A. Zero bias
B. Reverse bias
C. Alternating bias
D. Forward bias

8 What happens to the voltage across a Zener diode in its breakdown region?

Characteristics of Zener diode Easy
A. It remains nearly constant
B. It changes polarity repeatedly
C. It rises without limit
D. It falls steadily to zero

9 Which logic gate produces a HIGH output only when all its inputs are HIGH?

Logic gates Easy
A. OR gate
B. NOT gate
C. XOR gate
D. AND gate

10 Which logic gate reverses the logic state of a single input?

Logic gates Easy
A. NAND gate
B. NOT gate
C. OR gate
D. AND gate

11 A reverse-biased varactor diode mainly behaves as which circuit component?

Working and operation of Varactor diode Easy
A. Current source
B. Variable capacitor
C. Fixed resistor
D. Step-up transformer

12 A good diode tested with a multimeter should show which behavior?

Testing of diode and BJT Easy
A. High resistance forward and low resistance reverse
B. High resistance in both directions
C. Low resistance in both directions
D. Low resistance forward and high resistance reverse

13 When tested as diode junctions, which two junctions are present in a BJT?

Testing of diode and BJT Easy
A. Base-emitter and base-collector
B. Source-body and drain-body
C. Gate-source and gate-drain
D. Anode-cathode and gate-cathode

14 How many half-cycles of an AC input are used by a half-wave rectifier?

Half-wave rectifier Easy
A. Three half-cycles
B. Both half-cycles
C. Four half-cycles
D. One half-cycle

15 What is the ripple frequency of a full-wave rectifier supplied by an AC frequency of ?

Full-wave rectifier Easy
A.
B.
C.
D.

16 How many diodes are normally used in a single-phase full-wave bridge rectifier?

Full-wave bridge rectifier Easy
A. Six diodes
B. Four diodes
C. Two diodes
D. Three diodes

17 What are the three main terminals of a MOSFET?

MOSFET representation and characteristics Easy
A. Base, collector, and emitter
B. Gate, drain, and source
C. Anode, cathode, and gate
D. Input, output, and ground

18 Which is a common application of an ordinary PN junction diode?

Applications of diodes Easy
A. AC-to-DC rectification
B. Mechanical amplification
C. Magnetic field generation
D. Sound wave detection

19 Which is a common application of a transistor?

Applications of transistors Easy
A. Mechanical rotation
B. Thermal insulation
C. Light reflection
D. Signal amplification

20 What is the main function of a rectifier in a DC power supply?

Applications of rectifiers Easy
A. Convert AC into pulsating DC
B. Convert DC into steady AC
C. Increase the supply frequency
D. Store electrical charge

21 An intrinsic semiconductor is heated while the applied voltage remains constant. What happens to its current?

Introduction to semiconductor devices Medium
A. It increases because more charge carriers are generated
B. It remains constant because the material is intrinsic
C. It becomes zero because covalent bonds become stronger
D. It decreases because carrier mobility becomes zero

22 A silicon diode and a resistor are connected in series across a supply. If the diode is forward biased, what is the approximate circuit current?

Working and operation of PN junction diode Medium
A.
B.
C.
D.

23 A diode carries at room temperature. Using with , what is its small-signal resistance?

Characteristics of PN junction diode Medium
A.
B.
C.
D.

24 A Zener diode is used as a shunt regulator with a supply and a series resistor. With no load connected, what is the Zener current?

Working and operation of Zener diode Medium
A.
B.
C.
D.

25 A Zener diode voltage changes from to when its current changes from to . What is its dynamic resistance?

Characteristics of Zener diode Medium
A.
B.
C.
D.

26 Which single logic gate produces the same output as the expression ?

Logic gates Medium
A. NAND gate
B. AND gate
C. NOR gate
D. XOR gate

27 A warning indicator must turn on only when two digital sensor outputs are different. Which gate should be used?

Logic gates Medium
A. NOR gate
B. AND gate
C. XNOR gate
D. XOR gate

28 A varactor diode is used to tune an oscillator. What happens to its junction capacitance when the reverse-bias voltage is increased?

Working and operation of Varactor diode Medium
A. It remains fixed until breakdown occurs
B. It decreases as the depletion region widens
C. It becomes zero at the cut-in voltage
D. It increases as the depletion region widens

29 A silicon diode tested with a digital multimeter shows about in one direction and an open indication in the other. What does this result indicate?

Testing of diode and BJT Medium
A. The diode is open in both directions
B. The diode is operating in breakdown
C. The diode is internally shorted
D. The diode is operating normally

30 During diode-mode testing, one terminal of a BJT shows forward drops to both other terminals when the positive probe is connected to it. What does this indicate?

Testing of diode and BJT Medium
A. It is the base of an NPN transistor
B. It is the base of a PNP transistor
C. It is the emitter of a PNP transistor
D. It is the collector of an NPN transistor

31 An ideal half-wave rectifier receives a sinusoidal input with peak value . What is the average output voltage?

Half-wave rectifier Medium
A.
B.
C.
D.

32 A center-tapped full-wave rectifier is connected to a AC source. What is the fundamental ripple frequency at its output?

Full-wave rectifier Medium
A.
B.
C.
D.

33 A bridge rectifier receives a sinusoidal voltage with a peak of . If each conducting silicon diode drops , what is the peak load voltage?

Full-wave bridge rectifier Medium
A.
B.
C.
D.

34 An enhancement-mode n-channel MOSFET has . Which operating condition is most likely when ?

MOSFET representation and characteristics Medium
A. The MOSFET is in avalanche breakdown
B. The MOSFET is in the ohmic region
C. The MOSFET is in the cutoff region
D. The MOSFET is in the saturation region

35 For an enhancement n-channel MOSFET, in saturation. If , , and , what is ?

MOSFET representation and characteristics Medium
A.
B.
C.
D.

36 Why is a diode connected in reverse bias across a relay coil driven by a transistor?

Applications of diodes Medium
A. To double the voltage applied to the relay coil
B. To block the relay current during normal operation
C. To increase the transistor's forward current gain
D. To provide a path for the coil's induced current

37 A BJT is used to switch a load from a microcontroller output. In which regions should it ideally operate for efficient switching?

Applications of transistors Medium
A. Active and breakdown regions
B. Saturation and breakdown regions
C. Cutoff and active regions
D. Cutoff and saturation regions

38 A DC power supply must use both half-cycles of an AC source and does not have a center-tapped transformer. Which rectifier is most suitable?

Applications of rectifiers Medium
A. Single-diode half-wave rectifier
B. Zener shunt rectifier
C. Center-tapped full-wave rectifier
D. Full-wave bridge rectifier

39 Why is a power MOSFET often preferred over a BJT for high-frequency switching converters?

Applications of MOSFET Medium
A. It always has zero resistance in the ON state
B. It is voltage-controlled and switches rapidly
C. It can operate without any gate-drive voltage
D. It requires continuous base current during conduction

40 A Zener diode is rated at . Ignoring derating, what is the maximum safe Zener current?

Characteristics of Zener diode Medium
A.
B.
C.
D.

41 At , silicon has , electron mobility , and hole mobility . An uncompensated n-type sample has with complete ionization. Approximately how many times greater is its conductivity than that of intrinsic silicon?

Introduction to semiconductor devices Hard
A. times
B. times
C. times
D. times

42 A one-sided abrupt PN junction has a built-in potential of . Neglecting breakdown, by what factor does its depletion width change when the applied voltage changes from zero bias to reverse bias?

Working and operation of PN junction diode Hard
A. It increases by a factor of
B. It increases by a factor of
C. It increases by a factor of
D. It increases by a factor of

43 At , a diode current rises from to when its forward voltage rises by . Assuming both currents greatly exceed , what is the diode ideality factor?

Characteristics of PN junction diode Hard
A. Approximately
B. Approximately
C. Approximately
D. Approximately

44 Two reverse-biased silicon diodes are rated at and . Which statement most accurately describes their dominant breakdown mechanisms and temperature coefficients?

Working and operation of Zener diode Hard
A. Both devices are avalanche-dominated and have negative temperature coefficients
B. The device is avalanche-dominated with a positive coefficient; the device is tunneling-dominated with a negative coefficient
C. The device is tunneling-dominated with a negative coefficient; the device is avalanche-dominated with a positive coefficient
D. Both devices are tunneling-dominated and have positive temperature coefficients

45 An unloaded Zener regulator uses a series resistor. At its operating point, the Zener has dynamic resistance . If the supply increases by without changing the operating region, what is the approximate increase in output voltage?

Characteristics of Zener diode Hard
A.
B.
C.
D.

46 For the logic network which simplified expression is equivalent to ?

Logic gates Hard
A.
B.
C.
D.

47 A parallel resonant circuit contains a fixed capacitance in parallel with a varactor. Reverse-bias tuning changes the varactor capacitance from to while the inductance remains constant. What is the ratio of maximum to minimum resonant frequency?

Working and operation of Varactor diode Hard
A.
B.
C.
D.

48 In diode-test mode, a digital multimeter reads from red probe on terminal to black probe on , and from red probe on to black probe on . All reversed probe combinations read open circuit. What can be concluded reliably?

Testing of diode and BJT Hard
A. The device is PNP, is the emitter, and and are interchangeable
B. The device is NPN, is the base, and and require another test to distinguish collector from emitter
C. The device is NPN, is the collector, and is necessarily the emitter
D. The device is PNP, is the base, and is necessarily the collector

49 A half-wave rectifier has a sinusoidal source with peak voltage , diode forward resistance , and load resistance . Ignoring threshold voltage, what is its rectification efficiency, defined as DC load power divided by total AC input power?

Half-wave rectifier Hard
A.
B.
C.
D.

50 An ideal center-tapped full-wave rectifier has a peak voltage of from the center tap to either end of the secondary. With a resistive load, which pair gives the average output voltage and the peak inverse voltage of each diode?

Full-wave rectifier Hard
A. and
B. and
C. and
D. and

51 A bridge rectifier is supplied by an secondary and feeds a large smoothing capacitor under negligible load. Each conducting diode drops . Which pair most closely gives the capacitor voltage and the approximate peak inverse voltage per diode?

Full-wave bridge rectifier Hard
A. and
B. and
C. and
D. and

52 An enhancement n-channel MOSFET follows in the triode region, where and . What is for and ?

MOSFET representation and characteristics Hard
A.
B.
C.
D.

53 A MOSFET operating in saturation at fixed has drain current at and at . Using , estimate .

MOSFET representation and characteristics Hard
A.
B.
C.
D.

54 An inductive load is connected between and the drain of a low-side n-channel MOSFET. Where should an ordinary flyback diode be connected to protect the MOSFET during turn-off?

Applications of diodes Hard
A. Across the MOSFET, with cathode at ground and anode at the drain
B. In series with the load, with cathode toward the supply terminal
C. Across the load, with cathode at and anode at the drain
D. Across the load, with anode at and cathode at the drain

55 An NPN transistor driven by a logic output must switch a relay current. For a forced current gain of and , which listed base resistor is the largest value that satisfies the design requirement?

Applications of transistors Hard
A.
B.
C.
D.

56 A full-wave rectifier operating from a supply delivers a nearly constant load current to a smoothing capacitor. Neglecting conduction time and source resistance, what is the approximate peak-to-peak ripple voltage?

Applications of rectifiers Hard
A.
B.
C.
D.

57 A bootstrap gate driver is used with an n-channel MOSFET as the high-side switch of a half-bridge. Why can a conventional bootstrap supply generally not maintain the switch continuously on at duty cycle?

Applications of MOSFET Hard
A. The bootstrap capacitor cannot recharge unless the switch node periodically returns low
B. The high-side channel changes from n-type to p-type during continuous conduction
C. The MOSFET body diode permanently shorts the bootstrap capacitor at high duty cycle
D. The gate threshold voltage becomes zero when the drain remains at the supply voltage

58 Four NAND gates are connected as follows: , , , and . What function does implement?

Logic gates Hard
A.
B.
C.
D.

59 A Zener diode has a temperature coefficient of . A forward-biased silicon diode has a coefficient of . If they are placed in series with voltages adding, what is the approximate temperature behavior of the combined reference?

Characteristics of Zener diode Hard
A. A negative coefficient of at about
B. Nearly zero net coefficient at about
C. A positive coefficient of at about
D. Nearly zero net coefficient at about

60 During reverse recovery, a diode's reverse current is approximated by a triangular pulse with peak magnitude and total duration . If the recovered charge is , what is ?

Characteristics of PN junction diode Hard
A.
B.
C.
D.
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