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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 of the following is the most commonly used semiconductor material in electronic devices?

introduction to semiconductor devices Easy
A. Silicon
B. Aluminium
C. Mica
D. Copper

2 A pure semiconductor without any impurity added is known as a:

introduction to semiconductor devices Easy
A. N-type semiconductor
B. Extrinsic semiconductor
C. Intrinsic semiconductor
D. P-type semiconductor

3 In an N-type semiconductor, the majority charge carriers are:

introduction to semiconductor devices Easy
A. Protons
B. Electrons
C. Neutrons
D. Holes

4 When a PN junction diode is forward biased, the depletion region:

Working and operation of PN Junction diode Easy
A. Decreases in width
B. Becomes infinitely wide
C. Increases in width
D. Stays exactly the same

5 A PN junction diode primarily allows current to flow in:

Working and operation of PN Junction diode Easy
A. Only one direction
B. Both directions equally
C. Only alternating directions
D. No direction at all

6 The approximate forward voltage drop (knee voltage) of a silicon PN junction diode is about:

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

7 In the reverse-biased region of an ideal PN junction diode, the current is:

Characteristics of PN junction diode Easy
A. Equal to forward current
B. Nearly zero
C. Very large
D. Infinite

8 A Zener diode is normally operated in which region?

working and operation of Zener diode Easy
A. Cut-off region only
B. Saturation region
C. Forward conduction region
D. Reverse breakdown region

9 The main application of a Zener diode is as a:

working and operation of Zener diode Easy
A. Light emitter
B. Signal oscillator
C. Voltage regulator
D. Current amplifier

10 In the Zener breakdown region, the voltage across the Zener diode remains:

characteristics of Zener diode Easy
A. Rapidly increasing
B. Equal to zero
C. Steadily decreasing
D. Almost constant

11 Which logic gate produces an output of only when all its inputs are ?

logic gates Easy
A. OR gate
B. NOR gate
C. NOT gate
D. AND gate

12 A NOT gate is also commonly called a(n):

logic gates Easy
A. Inverter
B. Comparator
C. Buffer
D. Adder

13 The output of a two-input OR gate is only when:

logic gates Easy
A. Both inputs are
B. Both inputs are
C. Any input is
D. One input is

14 A varactor diode is used to provide a voltage-controlled:

Working and Operation of Varactor diode Easy
A. Frequency source
B. Capacitance
C. Resistance
D. Inductance

15 A varactor diode is normally operated under:

Working and Operation of Varactor diode Easy
A. Reverse bias
B. No bias at all
C. Forward bias
D. Zero bias only

16 When testing a good diode with a multimeter, it shows low resistance in forward direction and high resistance in reverse. A diode that reads low resistance in both directions is:

Testing of diode and BJT Easy
A. Reverse biased
B. Open
C. Shorted
D. Perfectly good

17 A half-wave rectifier conducts during:

Half wave and Full wave rectifier Easy
A. Both halves of the AC cycle
B. Only the negative peaks
C. The full cycle continuously
D. Only one half of the AC cycle

18 Compared to a half-wave rectifier, a full-wave rectifier has:

Half wave and Full wave rectifier Easy
A. The same single diode
B. No output voltage
C. Higher output efficiency
D. Lower output efficiency
E. A

19 How many diodes are used in a full-wave bridge rectifier?

Full wave bridge rectifier Easy
A. Two
B. Four
C. Six
D. One

20 What does the abbreviation MOSFET stand for?

MOSFET representation and characteristics Easy
A. Metal Only Semiconductor Fast Emitting Transistor
B. Metal Oxide Silicon Forward Emitter Transistor
C. Multiple Output Switching Field Effect Transistor
D. Metal Oxide Semiconductor Field Effect Transistor

21 A pure silicon crystal is doped with a pentavalent impurity such as phosphorus. What type of semiconductor is formed and what are the majority carriers?

introduction to semiconductor devices Medium
A. N-type with electrons as majority carriers
B. N-type with holes as majority carriers
C. Intrinsic semiconductor with equal electrons and holes
D. P-type with holes as majority carriers

22 When a PN junction diode is forward biased, what happens to the width of the depletion region and the potential barrier?

Working and operation of PN Junction diode Medium
A. Both increase, blocking current flow
B. Width increases but barrier decreases
C. Width decreases but barrier increases
D. Both decrease, allowing current to flow

23 In the V-I characteristics of a silicon PN junction diode, appreciable forward current begins only after the applied voltage exceeds approximately which value?

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

24 A Zener diode used for voltage regulation is always connected in which configuration in the circuit?

working and operation of Zener diode Medium
A. Forward biased and operated in saturation
B. Forward biased near its knee voltage
C. Reverse biased and operated in the breakdown region
D. Reverse biased but operated below breakdown

25 In the reverse breakdown region of a Zener diode's characteristic curve, how do voltage and current behave?

characteristics of Zener diode Medium
A. Both voltage and current decrease together
B. Both voltage and current increase proportionally
C. Voltage remains almost constant while current changes significantly
D. Voltage increases rapidly while current stays constant

26 A two-input logic gate produces a HIGH output only when both inputs are LOW. Which gate is this?

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

27 Using De Morgan's theorem, the expression is equivalent to which of the following?

logic gates Medium
A.
B.
C.
D.

28 A varactor diode is operated under reverse bias so that it behaves like a voltage-controlled capacitor. As the reverse voltage increases, what happens to its capacitance?

Working and Operation of Varactor diode Medium
A. Capacitance stays constant regardless of reverse voltage
B. Capacitance increases because the depletion width increases
C. Capacitance increases because the depletion width decreases
D. Capacitance decreases because the depletion width increases

29 While testing a diode with a digital multimeter in diode mode, a technician reads about in one direction and "OL" (open) when the leads are reversed. What is the condition of the diode?

Testing of diode and BJT Medium
A. The diode is good
B. The diode is leaky
C. The diode is open in both directions
D. The diode is shorted

30 When testing an NPN transistor with a multimeter, the base-emitter and base-collector junctions should behave like which arrangement of diodes?

Testing of diode and BJT Medium
A. Two diodes with their cathodes joined at the base
B. Two diodes with their anodes joined at the base
C. Two diodes connected in series between collector and emitter
D. A single diode between collector and emitter

31 A half-wave rectifier is supplied with a AC input. What is the ripple frequency of its output?

Half wave and Full wave rectifier Medium
A.
B.
C.
D.

32 A full-wave rectifier produces a peak output voltage of . What is the approximate average (DC) output voltage?

Half wave and Full wave rectifier Medium
A.
B.
C.
D.

33 What is the maximum theoretical rectification efficiency of a full-wave rectifier?

Half wave and Full wave rectifier Medium
A.
B.
C.
D.

34 In a full-wave bridge rectifier using a single transformer secondary of peak voltage , approximately what is the Peak Inverse Voltage (PIV) across each diode?

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

35 A key advantage of a bridge rectifier over a center-tapped full-wave rectifier is that it:

Full wave bridge rectifier Medium
A. Requires no transformer at all
B. Does not require a center-tapped transformer
C. Produces a higher ripple frequency
D. Uses only one diode

36 An enhancement-type N-channel MOSFET starts conducting between drain and source only when the gate-to-source voltage satisfies which condition?

MOSFET representation and characteristics Medium
A.
B.
C. (threshold voltage)
D.

37 In a MOSFET, the gate terminal controls the drain current but draws almost no DC current because:

MOSFET representation and characteristics Medium
A. The gate is made of a highly resistive metal
B. The gate forms a forward-biased PN junction
C. The gate is directly connected to the source
D. The gate is insulated from the channel by a thin oxide layer

38 In a power supply circuit, a capacitor is connected across the output of a rectifier. Its primary function is to:

Application of diodes, transistors, rectifiers and MOSFET Medium
A. Smooth the output by reducing ripple
B. Increase the peak output voltage indefinitely
C. Convert AC into DC
D. Rectify the negative half-cycles

39 A diode is placed across the coil of a relay in a circuit driven by a transistor. The purpose of this diode is to:

Application of diodes, transistors, rectifiers and MOSFET Medium
A. Increase the current flowing through the relay coil
B. Protect the transistor by suppressing the inductive voltage spike when the coil switches off
C. Act as a voltage regulator for the coil
D. Rectify the AC supply feeding the relay

40 The reverse saturation current of a PN junction diode is primarily due to:

Characteristics of PN junction diode Medium
A. Minority carriers crossing the junction
B. The barrier potential increasing
C. The applied forward voltage
D. Majority carriers crossing the junction

41 A silicon diode has a reverse saturation current at . Using the ideal diode equation with and ideality factor , what forward voltage is required to produce a current of ?

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

42 In a PN junction at equilibrium, the built-in potential barrier opposes diffusion of majority carriers. If the doping on both sides is increased by a factor of 10, how does the built-in potential change (temperature constant)?

Working and operation of PN Junction diode Hard
A. It increases by
B. It decreases by
C. It remains unchanged
D. It increases by

43 A Zener regulator uses a Zener with dynamic resistance . If the Zener current changes from to , what is the change in output (Zener) voltage?

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

44 In a shunt Zener regulator with , series resistor , and a Zener, what is the maximum load current the circuit can supply while keeping the Zener in regulation (ignore minimum Zener current)?

working and operation of Zener diode Hard
A. Approximately
B. Approximately
C. Approximately
D. Approximately

45 A half-wave rectifier delivers a peak output of into a resistive load. What is the ripple factor of the output?

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

46 A full-wave bridge rectifier is fed from a transformer secondary with RMS voltage . Assuming silicon diodes with drop each, what is the approximate DC output voltage (no filter)?

Full wave bridge rectifier Hard
A. Approximately
B. Approximately
C. Approximately
D. Approximately

47 For a full-wave bridge rectifier, how does the Peak Inverse Voltage (PIV) rating per diode compare to a center-tapped full-wave rectifier producing the same peak output ?

Full wave bridge rectifier Hard
A. Bridge PIV , center-tapped PIV
B. Both have PIV
C. Bridge PIV , center-tapped PIV
D. Both have PIV

48 A varactor diode has junction capacitance with and . What is at a reverse bias of ?

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

49 A logic function is given by . Which single gate is equivalent to ?

logic gates Hard
A. An AND gate
B. A NOR gate
C. A NOT gate on (i.e., )
D. An XOR gate

50 Using only 2-input NAND gates, what is the minimum number of NAND gates required to implement a 2-input XOR function?

logic gates Hard
A.
B.
C.
D.

51 An n-channel enhancement MOSFET has and (where in saturation). For and , what is ?

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

52 An n-channel MOSFET with operates with . At what maximum does the device remain in the triode (ohmic) region?

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

53 Using a digital multimeter in diode-test mode on a good silicon NPN transistor, which set of readings is expected?

Testing of diode and BJT Hard
A. Forward B-E and B-C both read ; C-E reads open both ways
B. Forward B-E reads and B-C reads open
C. B-E and B-C read open in both directions; C-E reads
D. All three junctions read in both directions

54 A diode under test shows a low resistance reading (near ) in BOTH forward and reverse directions with an ohmmeter. What is the most likely condition?

Testing of diode and BJT Hard
A. The diode is shorted
B. The diode is leaky but usable
C. The diode is healthy
D. The diode is open

55 The reverse saturation current of a silicon diode approximately doubles for every rise. If at , what is at ?

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

56 A full-wave rectifier (center-tapped) and a half-wave rectifier both produce the same peak voltage . What is the ratio of their DC output voltages (full-wave to half-wave)?

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

57 In a diode clamper circuit, a capacitor charges to the peak input voltage and shifts the DC level of the signal. For a positive clamper with input sine and an ideal diode, what are the output voltage limits?

Application of diodes, transistors, rectifiers and MOSFET Hard
A. to
B. to
C. to
D. to

58 Intrinsic silicon has . If it is doped with donors at , what is the approximate equilibrium hole concentration ?

introduction to semiconductor devices Hard
A.
B.
C.
D.

59 Below approximately , Zener diodes break down mainly by one mechanism, and above approximately by another. Which statement correctly describes their temperature coefficients?

working and operation of Zener diode Hard
A. Zener breakdown () has negative tempco; avalanche () has positive tempco
B. Zener breakdown has positive tempco; avalanche has negative tempco
C. Both mechanisms have positive temperature coefficients
D. Both mechanisms have negative temperature coefficients

60 A capacitor-filtered full-wave rectifier supplies a load drawing from a capacitor at a line frequency of . What is the approximate peak-to-peak ripple voltage?

Application of diodes, transistors, rectifiers and MOSFET Hard
A.
B.
C.
D.
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