ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-ELECTRONIC DEVICES AND CIRCUITS

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

A. holes
B. electrons
C. ions
D. holes and electrons

Answer: D

2. Work function is the maximum energy required by the fastest electron
at 0 K to escape from the metal surface.

A. True
B. False

Answer: B

3. The most commonly used semiconductor material is

A. silicon
B. germanium
C. mixture of silicon and germanium
D. none of the above

Answer: A

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

A. Zener diode
B. Tunnel diode
C. Schottky diode
D. PIN diode

Answer: C

5. 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

Answer: A

6. 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

Answer: B

7. 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

Answer: A

8. Voltage series feedback (Also called series-shunt feedback) results in

A. increase in both I/P and O/P impedances
B. decrease in both I/P and O/P impedances
C. increase in I/P impedance and decrease in O/P impedance
D. decrease in I/P impedance and increase in O/P impedance

Answer: C

9. How many free electrons does a p type semiconductor has?

A. only those produced by thermal energy
B. only those produced by doping
C. those produced by doping as well as thermal energy
D. any of the above

Answer: A

10. Which of the following has highest resistivity?

A. Mica
B. Paraffin wax
C. Air
D. Mineral oil

Answer: C

11. Assertion (A): In p-n-p transistor collector current is termed
negative.

Reason (R): In p-n-p transistor holes are majority carriers.

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

Answer: B

12. The sensitivity of human eyes is maximum at

A. white portion of spectrum
B. green portion of spectrum
C. red portion of spectrum
D. violet portion of spectrum

Answer: B

13. In a bipolar transistor, the base collector junction has

A. forward bias
B. reverse bias
C. zero bias
D. zero or forward bias

Answer: B

14. An intrinsic silicon sample has 1 million free electrons at room
temperature. As the temperature is increased

A. the number of free electrons increases
B. the number of free electrons increases but the number of holes decreases
C. the number of free electrons and holes increase by the same amount
D. the number of free electrons and holes increase but not by the same amount

Answer: C

15. What is the necessary a.c. input power from the transformer secondary
used in a half wave rectifier to deliver 500 W of d.c. power to the load?

A. 1232 W
B. 848 W
C. 616 W
D. 308 W

Answer: A

16. In a semi-conductor diode, the barrier offers opposition to

A. holes in P-region only
B. free electrons in N-region only
C. majority carriers in both regions
D. majority as well as minority carriers in both regions

Answer: C

17. In a half wave rectifier, the load current flows

A. only for the positive half cycle of the input signal
B. only for the negative half cycle of the input signal
C. for full cycle
D. for less than fourth cycle

Answer: A

18. For a 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

19. Assertion (A): A VMOS can handle much larger current than other field
effect transistors.

Reason (R): In a VMOS the conducting channel is very narrow.

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

Answer: C

20. In monolithic ICs, all the components are fabricated by

A. diffusion process
B. oxidation
C. evaporation
D. none

Answer: A

21. Which one of the following is not a characteristic of a ferroelectric
material?

A. High dielectric constant
B. No hysteresis
C. Ferroelectric characteristic only above the curie point
D. Electric dipole moment

Answer: C

22. In the sale of diamonds the unit of weight is carat. One carat is
equal to

A. 100 mg
B. 150 mg
C. 200 mg
D. 500 mg

Answer: C

23. Assertion (A): A JFET can be used as a current source.

Reason (R): In beyond pinch off region the current in JFET is nearly
constant.

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

Answer: A

24. Permalloy is

A. a variety of stainless steel
B. a polymer
C. a conon-ferrous alloy used in aircraft industry
D. a nickel an iron alloy having high permeability

Answer: D

25. Which of the following could be the maximum current rating of
junction diode by 126?

A. 1 A
B. 10 A
C. 20 A
D. 100 A

Answer: A

26. Each cell of a static Random Access memory contains

A. 6 MOS transistor
B. 4 MOS transistor, 2 capacitor
C. 2 MOS transistor, 4 capacitor
D. 1 MOS transistor and 1 capacitor

Answer: A

27. An electron in the conduction band

A. has higher energy than the electron in the valence band
B. has lower energy than the electron in the valence band
C. loses its charge easily
D. jumps to the top of the crystal

Answer: A

28. The dynamic resistance of a forward biased p-n diode

A. varies inversely with current
B. varies directly with current
C. is constant
D. is either constant or varies directly with current

Answer: A

29. A thermistor is a

A. thermocouple
B. thermometer
C. miniature resistance
D. heat sensitive explosive

Answer: C

30. When diodes are connected in series to increase voltage rating the
peak inverse voltage per junction

A. should not exceed half the breakdown voltage
B. should not exceed the breakdown voltage
C. should not exceed one third the breakdown voltage
D. may be equal to or less than breakdown voltage

Answer: C

31. Hall effect is observed in a specimen when it is carrying current and
is placed in a magnetic field. The resultant electric field inside the specimen
is

A. normal to both current and magnetic field
B. in the direction of current
C. antiparallel to magnetic field
D. in arbitrary direction

Answer: A

32. In an ideal diode there is no breakdown, no __________ current, and
no forward __________ drop.

A. reverse, voltage
B. forward, current
C. forward, voltage
D. reverse, current

Answer: A

33. Silicon is not suitable for fabrication of light emitting diodes
because it is

A. an indirect band gap semiconductor
B. direct band gap semiconductor
C. wideband gap semiconductor
D. narrowband gap semiconductor

Answer: A

34. MOSFET can be used as a

A. current controlled capacitor
B. voltage controlled capacitor
C. current controlled inductor
D. voltage controlled inductor

Answer: B

35. Power diodes are generally

A. silicon diodes
B. germanium diodes
C. either of the above
D. none of the above

Answer: A

36. The depletion layer width of Junction

A. decreases with light doping
B. is independent of applied voltage
C. is increased under reverse bias
D. increases with heavy doping

Answer: C

37. Forbidden energy gap in germanium at 0 K is about

A. 10 eV
B. 5 eV
C. 2 eV
D. 0.78 eV

Answer: D

38. Light dependent resistors are

A. highly doped semiconductor
B. intrinsic semiconductor
C. lightly doped semiconductor
D. either (a) or (c)

Answer: C

39. Fermi level is the amount of energy in which

A. a hole can have at room temperature
B. an electron can have at room temperature
C. must be given to an electron move to conduction band
D. none of the above

Answer: C

40. When avalanche breakdown occurs covalent bonds are not affected.

A. True
B. False

Answer: B

41. An ideal Op-amp is an ideal

A. voltage controlled current source
B. voltage controlled voltage source
C. current controlled current source
D. current controlled voltage source

Answer: B

42. Free electrons exist in

A. first band
B. second band
C. third band
D. conduction band

Answer: D

43. As compared to bipolar junction transistor, a FET

A. is less noisy
B. has better thermal stability
C. has higher input resistance
D. all of the above

Answer: D

44. For a P-N diode, the number of minority carriers crossing the
junction depends on

A. forward bias voltage
B. potential barrier
C. rate of thermal generation of electron hole pairs
D. none of the above

Answer: C

45. Which variety of copper has the best conductivity?

A. Pure annealed copper
B. Hard drawn copper
C. Induction hardened copper
D. Copper containing traces of silicon

Answer: A

46. The output, V-I characteristics of an Enhancement type MOSFET has

A. only an ohmic region
B. only a saturation region
C. an ohmic region at low voltage value followed by a saturation region at
higher voltages
D. an ohmic region at large voltage values preceded by a saturation region at
lower voltages

Answer: C

47. Piezoelectric quartz crystal resonators find application where

A. signal amplification is required
B. rectification of the signal is required
C. signal frequency control is required
D. modulation of signal is required

Answer: B

48. The forbidden energy gap between the valence band and conduction band
will be least in case of

A. metals
B. semiconductors
C. insulators
D. all of the above

Answer: A

49. If too large current passes through the diode

A. all electrons will leave
B. all holes will freeze
C. excessive heat may damage the diode
D. diode will emit light

Answer: C

50. In a bipolar transistor, the emitter base junction has

A. forward bias
B. reverse bias
C. zero bias
D. zero or reverse bias

Answer: A
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