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Semiconductor Mcq Question Set 3
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1. The impurity level in an extrinsic semiconductor is about …….. of pure semiconductor.
10 atoms for 108 atoms
1 atom for 108 atoms
1 atom for 104 atoms
1 atom for 100 atoms
2. As the doping to a pure semiconductor increases, the bulk resistance of the semiconductor ……..
remains the same
increases
decreases
none of the above
3. A hole and electron in close proximity would tend to ……..
repel each other
attract each other
have no effect on each other
none of the above
4. In a semiconductor, current conduction is due ……..
only to holes
only to free electrons
to holes and free electrons
none of the above Answer: to holes and free electrons
5. The random motion of holes and free electrons due to thermal agitation is called ……..
diffusion
pressure
ionisation
none of the above
6. A forward biased pn junction has a resistance of the ……..
order of Ω
order of kΩ
order of MΩ
none of the above
7. The battery connections required to forward bias a pn junction are ……..
+ve terminal to p and −ve terminal to n
−ve terminal to p and +ve terminal to n
−ve terminal to p and −ve terminal to n
none of the above
8. The barrier voltage at a pn junction for germanium is about ……..
3.5 V
3V
zero
0.3 V
9. In the depletion region of a pn junction, there is a shortage of ……….
acceptor ions
holes and electrons
donor ions
none of the above
10. A reverse biased pn junction has ……..
very narrow depletion layer
almost no current
very low resistance
large current flow
11. A pn junction acts as a ……..
controlled switch
bidirectional switch
unidirectional switch
none of the above
12. A reverse biased pn junction has resistance of the……..
order of Ω
order of kΩ
order of MΩ
none of the above
13. The leakage current across a pn junction is due to ……..
minority carriers
majority carriers
junction capacitance
none of the above
14. When the temperature of an extrinsic semiconductor is increased, the pronounced effect is on ……..
junction capacitance
minority carriers
majority carriers
none of the above
15. With forward bias to a pn junction, the width of depletion layer ……..
decreases
increases
remains the same
none of the above
16. The leakage current in a pn junction is of the order of ……..
A
mA
kA
μA
17. In an intrinsic semiconductor, the number of free electrons ……..
equals the number of holes
is greater than the number of holes
is less than the number of holes
none of the above
18. At room temperature, an intrinsic semiconductor has ……..
many holes only
a few free electrons and holes
many free electrons only
No holes or free electrons
19. At absolute temperature, an intrinsic semiconductor has …….
a few free electrons
many holes
many free electrons
No holes or free electrons
20. At room temperature, an intrinsic silicon crystal acts approximately as ……..
a battery
a conductor
an insulator
A piece of copper wire
21. Which among the following is the most commonly used semiconductor?
Silicon
Carbon
Germanium
Sulphur
22. What happens to the resistance of a pure semiconductor when heated?
The resistance increases
The resistance decreases
The temperature remains the same
Can’t say
23. How many valence electrons does a pentavalent impurity have?
3
4
5
6
24. How many valence electrons do trivalent impurities have?
2
3
4
5
25. Which of the following is created when trivalent impurities are added to a semiconductor?
Free electrons
Holes
Bound electrons
Valence electrons
26. Which of the following does a hole in the semiconductor define?
A free proton
A free neutron
A free-electron
An incomplete part of an electron pair bond
27. An electron and a hole in close proximity would tend to _____.
attract each other
repel each other
have no effect on each other
destroy each other
28. An electron and a hole in close proximity would tend to _____.
attract each other
repel each other
have no effect on each other
destroy each other
29. What is the random motion of free electrons and holes due to thermal agitation called?
Pressure
Diffusion
Ionisation
none of the above
30. Why is the mobility of free electrons greater than that of holes?
They are light
They mutually collide less
They require low energy to continue the motion
They carry negative energy
31. Which of the following does the resistivity of a semiconductor depend upon?
Length of the semiconductor
Atomic nature of the semiconductor
Shape and atomic nature of the semiconductor
Shape of semiconductor
32. Which of the following statements is true about extrinsic semiconductors?
The gap between the conduction band and the valence bond is more than 16 eV
The gap between the conduction band and the valence bond is about 1 eV
The gap between the conduction band and valence band is 100 eV and more
The conduction band and the valence band overlap.
33. In a semiconductor
there are no free electrons at 0 K
there are no free electrons at any temperature
the number of free electrons increases with pressure
the number of free electrons is more than that in a conductor
34. Let nh and ne be the number of holes and conduction electrons in an extrinsic semiconductor. Then
nh > ne
nh = ne
nh < ne
nh ≠ ne
35. Electric conduction in a semiconductor takes place due to
electrons only
holes only
both electrons and holes
neither electrons nor holes
36. The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of
phosphorus
boron
antimony
nitrogen
37. The electrical conductivity of pure germanium can be increased by
increasing the temperature
doping acceptor impurities
doping donor impurities
All of the above
38. The resistivity of a semiconductor at room temperature is in between
10–2 to 10–5 Ω cm
10–3 to 106 Ω cm
106 to 108 Ω cm
1010 to 1012 Ω cm
39. In a semiconductor, the forbidden energy gap between the valence band and the conduction band is of the order is
1 MeV
0.1 Mev
1 eV
5 eV
40. The forbidden energy gap for germanium crystal at 0 K is
0.071 eV
0.71 eV
2.57 eV
6.57 eV
41. In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of
1 MeV
0.1 MeV
1 eV
5 eV
42. What is the resistivity of a pure semiconductor at absolute zero ?
Zero
Infinity
Same as that of conductors at room temperature
Same as that of insulators at room temperature
43. Temperature coefficient of resistance of semiconductor is
zero
constant
positive
Negative
44. In a p-type semiconductor, the acceptor valence band is
close to the valence band of the host crystal
close to conduction band of the host crystal
below the conduction band of the host crystal
above the conduction band of the host crystal
45. In an n-type semiconductor, donor valence band is
above the conduction band of the host crystal
close to the valence band of the host crystal
close to the conduction band of the host crystal
below the valence band of the host crystal
46. The mobility of free electrons is greater than that of free holes because
they are light
they carry negative charge
they mutually collide less
they require low energy to continue their motion
47. The relation between number of free electrons (n) in a semiconductor and temperature (T) is given by
n α T
n α T2
n α √T
n α T3/2
48. In semiconductors, at room temperature
the conduction band is completely empty
the valence band is partially empty and the conduction band is partially filled
the valence band is completely filled and the conduction band is partially filled
the valence band is completely filled
49. At absolute zero, Si acts as
non-metal
metal
insulator
None of these
50. One serious drawback of semi-conductor devices is
they do not last for long time.
they are costly
they cannot be used with high voltage.
they pollute the environment.
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