# 35 prime semiconductor theory questions and answers

1. A semiconductor is formed by ……… bonds.
A. Covalent
B. Electrovalent
C. Co-ordinate
D. None of the above
ANS:- A
2. A semiconductor has ………… temperature coefficient of resistance.
Positive
Zero
Negative
None of the above
ANS:- C
3. The most commonly used semiconductor is ………..
Germanium
Silicon
Carbon
Sulphur
ANS:- B

4. A semiconductor has generally ……………… valence electrons.
23
64
ANS:- D
5. The resistivity of pure germanium under standard conditions is
6 x 104
O cm
60
O cm
3 x 106
O cm
6 x 10-4
O cm
ANS:- B
6. The resistivity of a pure silicon is about ……………
100 O cm
6000 O cm
3 x 105 O m
6 x 10-8 O cm
ANS:- B
7. When a pure semiconductor is heated, its resistance …………..
Goes up
Goes down
Remains the same
Can’t say
ANS:- B
8. The strength of a semiconductor crystal comes from ……..
Forces between nuclei
Forces between protons
Electron-pair bonds
None of the above
ANS:- C
9. When a pentavalent impurity is added to a pure semiconductor, it
becomes ………
An insulator
An intrinsic semiconductor
p-type semiconductor
n-type semiconductor
ANS:- D
10. Addition of pentavalent impurity to a semiconductor creates
many ……..
Free electrons
Holes
Valence electrons
Bound electrons
ANS:- A
11. A pentavalent impurity has ………. Valence electrons
35
4
6
ANS:- B
12. An n-type semiconductor is ………
Positively charged
Negatively charged
Electrically neutral
None of the above
ANS:- C
13. A trivalent impurity has ….. valence electrons
45
63
ANS:- D
14. Addition of trivalent impurity to a semiconductor creates
many ……..
Holes

Free electrons
Valence electrons
Bound electrons
ANS:- A
15. A hole in a semiconductor is defined as …………….
A free electron
The incomplete part of an electron pair bond
A free proton
A free neutron
ANS:- B
16. 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
ANS:- B
17. As the doping to a pure semiconductor increases, the bulk
resistance of the semiconductor ………..
Remains the same
Increases
Decreases
None of the above
ANS:- C
18. 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
ANS:- B
19. In a semiconductor, current conduction is due to ……..
Only holes
Only free electrons
Holes and free electrons
None of the above
ANS:- C
20. The random motion of holes and free electrons due to thermal
agitation is called ……….
Diffusion
Pressure
Ionisation
None of the above
ANS:- A
21. A forward biased pn junction diode has a resistance of the order of
Ok
O
MO
None of the above
ANS:- A
22. 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
ANS:- A
23. The barrier voltage at a pn junction for germanium is about ………
5 V
3 V
Zero
3 V
ANS:- D
24. In the depletion region of a pn junction, there is a shortage of ……..
Acceptor ions
Holes and electrons
Donor ions
None of the above
ANS:- B
25. A reverse bias pn junction has …………
Very narrow depletion layer
Almost no current
Very low resistance
Large current flow
ANS:- B
26. A pn junction acts as a ……….
Controlled switch
Bidirectional switch
Unidirectional switch
None of the above
ANS:- C
27. A reverse biased pn junction has resistance of the order of
Ok
O
MO
None of the above
ANS:- C
28. The leakage current across a pn junction is due to …………..
Minority carriers
Majority carriers
Junction capacitance
None of the above
ANS:- A

29. When the temperature of an extrinsic semiconductor is increased,
the pronounced effect is on……
Junction capacitance
Minority carriers
Majority carriers
None of the above
ANS:- B
30. With forward bias to a pn junction , the width of depletion
layer ………
Decreases
Increases
Remains the same
None of the above
ANS:- A
31. The leakage current in a pn junction is of the order of
Aa
mA
kA
μA
ANS:- D
32. 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
ANS:- A
33. 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
ANS:- B
34. At absolute temperature, an intrinsic semiconductor has ……….
A few free electrons
Many holes
Many free electrons
No holes or free electrons
ANS:- D
35. At room temperature, an intrinsic silicon crystal acts
approximately as ……
A battery
A conductor
An insulator
A piece of copper wire
ANS:- C