SemiConductors Quiz

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SemiConductors Quiz

Quiz

1. In a p-n junction
(a) the potential of p & n sides becomes higher alternately
(b) the p side is at higher electrical potential than n side
(c) the n side is at higher electric potential than p side
(d) both p & n sides are at same potential
Ans:b

2. Barrier potential of a p-n junction diode does not depend on
(a) doping density
(b) diode design
(c) temperature
(d) forward bias
Ans:b

3. The energy band gap is maximum in
(a) metals
(b) superconductors
(c) insulators
(d) semiconductors
Ans:c

4. The part of a transistor which is most heavily doped to produce large number of majority carriers is
(a) emmiter
(b) base
(c) collector
(d) can be any of the above three
Ans: a

5. When n-p-n transistor is used as an amplifier
(a) electrons move from collector to base
(b) holes move from emitter to base
(c) electrons move from base to collector
(d) holes move from base to emitter
Ans:d

6. In a common base amplifier the phase difference between the input signal voltage and the output voltage is
(a) 0
(b) $$\frac {π}{4}$$

(c) $$\frac {π}{2}$$

(d) $$π$$
Ans:a

7. Inverter converts
(a) alternating current into direct current
(b) direct current into alternating current
(c) current at low voltage to current at high voltage
(d) None of these
Ans:b

8. The Donor level in a semiconductor is placed
(a) half-way in the forbidden energy gap
(b) in the forbidden energy gap close to the upper edge of the valence band
(c) in the conduction band close to the lower edge to the conduction band
(d) in the forbidden energy gap close to the lower edge of the conduction band
Ans: d

9. If the distance between the conduction band and valence band is 1 eV. This combination is
(a) semiconductor
(b) conductor
(c) metal
(d) insulator
Ans:a

10. Carbon, silicon and germanium have four valence electrons
each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to $$(E_g)_c ,(E_g)_{si}, (E_g)_{Ge}$$. Which of the following statements is true?

(a)$$(E_g)_{si}<(E_g)_{Ge}<(E_g)_c$$

(b)$$(E_g)_c<(E_g)_{Ge}<(E_g)_{si}$$

(c)$$(E_g)_c<(E_g)_{si}<(E_g)_{Ge}$$

(d)$$(E_g)_c = (E_g)_{si} = (E_g)_{Ge}$$
Ans:c

11. In an unbiased p-n junction, holes diffuse from the p-region to n-region because
(a) free electrons in the n-region attract them.
(b) they move across the junction by the potential difference.
(c) hole concentration in p-region is more as compared to n-region.
(d) all the above
Ans:c

12. For a transistor amplifier, the voltage gain
(a) remains constant for all frequencies.
(b) is high at high and low frequencies and constant in the middle frequency range.
(c) is low at high and low frequencies and constant at mid frequencies.
(d) none of the above
Ans:c

13. p-n junction diode works as a insulator, if connected
(a) to A.C.
(b) in forward bias
(c) in reverse bias
(d) None of these
Ans:c

14. In an n-type silicon, which of the following statement is true?
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atoms are the dopants.
(c) Holes are minority carriers and pentavalent atoms are the dopants.
(d) Holes are majority carriers and trivalent atoms are the dopants.
Ans: c

15. Which of the statements is true for p-type semiconductos?
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atoms are the dopants.
(c) Holes are minority carriers and pentavalent atoms are the dopants.
(d) Holes are majority carriers and trivalent atoms are the dopants.
Ans:d

16. When a forward bias is applied to a p-n junction, it
(a) raises the potential barrier.
(b) reduces the majority carrier current to zero.
(c) lowers the potential barrier.
(d) None of these
Ans:c

17. The potential barrier, in the depletion layer, is due to
(a) ions
(b) holes
(c) electrons
(d) both (b) and (c)
Ans:a

18. Zener diode is used as
(a) half wave rectifier
(b) full wave rectifier
(c) A.C. voltage stabilizer
(d) D.C. voltage stabilizer
Ans: c

19. For a transistor amplifier, the voltage gain
(a) remains constant for all frequencies
(b) is high at high and low frequencies and constant in the middle frequency range
(c) is low at high and low frequencies and constant at mid frequencies
(d) None of these
Ans: c

20. In a semiconductor, the concentration of electrons is $$8 × 10^{14} cm^3$$ and that of the holes $$5 × 10^{12} cm^3$$. The semiconductor is
(a) p-type
(b) n-type
(c) intrinsic
(d) Cannot say
Ans:b

21. When a semiconductor is heated, its resistance
(a) decreases
(b) increases
(c) remains unchanged
(d) either (b) or (c)
Ans:a

22. The forbidden gap in the energy bands of germanium at room temperature is about
(a) 1.1 eV (b) 0.1 eV
(c) 0.67 eV (d) 6.7 eV
Ans:c

23. To obtain a p-type germanium semiconductor, it must be doped with
(a) arsenic
(b) antimony
(c) indium
(d) phosphorus
Ans:c

24. Which impurity is doped in Si to form n-type semiconductors?
(a) Al
(b) B
(c) As
(d) None of these
Ans:c

25. In extrinsic semiconductors
(a) the conduction band and valence band overlap
(b) the gap between conduction band and valence band is more than 16 eV
(c) the gap between conduction band and valence band is near about 1 eV
(d) the gap between conduction band and valence band
will be 100 eV and more
Ans:c

26. Function of rectifier is
(a) to convert A.C. into D.C.
(b) to convert D.C. into A.C.
(c) Both (a) and (b)
(d) None of these
Ans: a

27. Zener breakdown takes place if
(a) doped impurity is low
(b) doped impurity is high
(c) less impurity in n-part
(d) less impurity in p-part
Ans:b

28. Which one of the following is not a correct statement about semiconductors?
(a) The electrons and holes have different mobilities in a semiconductor
(b) In an n-type semiconductor, the Fermi level lies closer to the conduction band edge
(c) Silicon is a direct band gap semiconductor
(d) Silicon is has diamond structure
Ans:c

29. The energy band gap is minimum in
(a) metals
(b) superconductors
(c) insulators
(d) semiconductors.
Ans: a

30. An oscillator is nothing but an amplifer with
(a) positive feedback
(b) negative feedback
(c) large gain
(d) no feedback
Ans:a

31. When a solid with a band gap has a donor level just below its empty energy band, the solid is
(a) an insulator
(b) a conductor
(c) p-type semiconductor
(d) n-type semiconductor
Ans: d

32. Regarding a semiconductor which one of the following is wrong?
(a) There are no free electrons at room temperature
(b) There are no free electrons at 0K
(c) The number of free electrons increases with rise of temperature
(d) The charge carriers are electrons and holes
Ans:a

33. p-n junction is said to be forward biased, when
(a) the positive pole of the battery is joined to the p-semiconductor and negative pole to the n-semiconductor
(b) the positive pole of the battery is joined to the n-semiconductor and p-semiconductor
(c) the positive pole of the battery is connected to n- semiconductor and p- semiconductor
(d) a mechanical force is applied in the forward direction
Ans: a

34. At absolute zero, Si acts as
(a) non-metal
(b) metal
(c) insulator
(d) None of these
Ans:c

35. When n-type semiconductor is heated
(a) number of electrons increases while that of holes decreases
(b) number of holes increases while that of electrons decreases
(c) number of electrons and holes remain same
(d) number of electrons and holes increases equally
Ans:d

36. To use a transistor as an amplifier
(a) The emitter base junction is forward biased and the base collector junction is reverse biased
(b) no bias voltage is required
(c) both junctions are forward biased
(d) both junctions are reverse biased
Ans:a

37. The part of the transistor which is heavily doped to produce large number of majority carriers is
(a) emitter
(b) base
(c) collector
(d) any of the above depending upon the nature of transistor
Ans:a

38. When a p-n junction diode is reverse biased the flow of current across the junction is mainly due to
(a) diffusion of charges
(b) drift of charges
(c) depends on the nature of material
(d) both drift and diffusion of charges
Ans:b

39. When an n–p–n transistor is used as an amplifier then
(a) electrons flow from emitter to collector
(b) holes flow from emitter to collector
(c) electrons flow from collector to emitter
(d) electrons flow from battery to emitter
Ans:a

40. An n-p-n transistor conducts when
(a) both collector and emitter are negative with respect to the base
(b) both collector and emitter are positive with respect to the base
(c) collector is positive and emitter is negative with respect to the base
(d) collector is positive and emitter is at same potential as the base
Ans: c

41. Reverse bias applied to a junction diode
(a) increases the minority carrier current
(b) lowers the potential barrier
(c) raises the potential barrier
(d) increases the majority carrier current
Ans:c

42. In semiconductors, at room temperature
(a) the conduction band is completely empty
(b) the valence band is partially empty and the conduction band is partially filled
(c) the valence band is completely filled and the conduction band is partially filled
(d) the valence band is completely filled
Ans:c

43. Application of a forward bias to a p–n junction
(a) widens the depletion zone.
(b) increases the potential difference across the depletion zone.
(c) increases the number of donors on the n side.
(d) increases the electric field in the depletion zone.
Ans: c

44. A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of
(a) each of them increases
(b) each of them decreases
(c) copper increases and germanium decreases
(d) copper decreases and germanium increases
Ans: d

45. In an intrinsic semiconductor
(a) only electrons are responsible for flow of current
(b) both holes and electrons carry current
(c) both holes and electrons carry current with electrons being majority carriers
(d) only holes are responsible for flow of current
Ans:b

46. If the conductivity of a semiconductor is only due to break up of the covalent bonds due to thermal excitation, then the semiconductor is called
(a) intrinsic
(b) extrinsic
(c) donor
(d) acceptor
Ans:a

47. The mobility of conduction electrons is greater than that of holes, since electrons
(a) are lighter
(b) are negatively charged
(c) require smaller energy for moving through crystal lattice
(d) undergo smaller number of collisions
Ans:c

48. In the symbol of a transistor , the arrow head points in the direction of flow of
(a) holes
(b) electrons
(c) majority carriers
(d) minority carriers
Ans: a

49. Transistors are essentially
(a) power driven devices
(b) current driven devices
(c) voltage driven devices
(d) resistance driven devices
Ans:b

50. In a transistor
(a) emitter is more highly doped than collector
(b) collector is more highly doped than emitter
(c) both are equally doped
(d) None of the above
Ans: a

51. One way in which the operation of an n-p-n transistor differs from that of a p-n-p
(a) the emitter junction is reverse biased in n-p-n.
(b) the emitter junction injects minority carriers into base region of the p-n-p
(c) the emitter injects holes into the base of the p-n-p and electrons into the base region n-p-n
(d) the emitter injects holes into the base of n-p-n
Ans:c

52. n-p-n transistors are preferred to p-n-p transistors because:
(a) they have low cost
(b) they have low dissipation energy
(c) they are capable of handling large power
(d) electrons have high mobility than holes and hence high mobility of energy
Ans: d

53. An alternating current can be converted into direct current by a
(a) rectifier
(b) transformer
(c) dynamo
(d) motor
Ans:a