1. A semiconductor is formed by ........ bonds.

(i) covalent (ii) electrovalent

(iii) co-ordinate (iv) none of the above
2. A semiconductor has ........ temperature
coefficient of resistance.
(i) positive (ii) zero
(iii) negative (iv) none of the above
3. The most commonly used semiconductor isٍ‫س‬
........
(i) germanium (ii) silicon
(iii) carbon (iv) sulphur
4. A semiconductor has generally ........
valence electrons.
(i) 2 (ii) 3
(iii) 6 (iv) 4
5. The resistivity of pure germanium under
standard conditions is about ........
(i) 6 ⋅ 104 Ω cm (ii) 60 Ω cm

(iii) 3 ⋅ 106 Ω cm (iv) 6 ⋅ 10−4 Ω cm

6. The resistivity of pure silicon is about ........
(i) 100 Ω cm (ii) 6000 Ω cm

(iii) 3 ⋅ 105 Ω cm (iv) 1.6 ⋅ 10− 8 Ω cm

7. When a pure semiconductor is heated, its
resistance ........
(i) goes up (ii) goes down
(iii) remains the same (iv) cannot say
8. The strength of a semiconductor crystal
comes from ........
(i) forces between nuclei
(ii) forces between protons
(iii) electron-pair bonds
(iv) none of the above
9. When a pentavalent impurity is added to a
pure semiconductor, it becomes ........
(i) an insulator
(ii) an intrinsic semiconductor
(iii) p-type semiconductor
(iv) n-type semiconductor
10. Addition of pentavalent impurity to a semiconductor
creates many ........
(i) free electrons (ii) holes
(iii) valence electrons
(iv) bound electrons
11. A pentavalent impurity has ........ valence
electrons.
(i) 3 (ii) 5
(iii) 4 (iv) 6

12. An n-type semiconductor is ........

(i) positively charged
(ii) negatively charged
(iii) electrically neutral
(iv) none of the above
13. A trivalent impurity has ........ valence
electrons.
(i) 4 (ii) 5
(iii) 6 (iv) 3
14. Addition of trivalent impurity to a semiconductor
creates many ........
(i) holes (ii) free electrons
(iii) valence electrons
(iv) bound electrons
15. A hole in a semiconductor is defined as ........
(i) a free electron
(ii) the incomplete part of an electron pair
bond
(iii) a free proton
(iv) a free neutron
16. The impurity level in an extrinsic semiconductor
is about ........ of pure semiconductor.
(i) 10 atoms for 108 atoms
(ii) 1 atom for 108 atoms
(iii) 1 atom for 104 atoms
(iv) 1 atom for 100 atoms
17. As the doping to a pure semiconductor
increases, the bulk resistance of the
semiconductor ........
(i) remains the same
(ii) increases
(iii) decreases
(iv) none of the above
18. A hole and electron in close proximity would
tend to ........
(i) repel each other
(ii) attract each other
(iii) have no effect on each other
(iv) none of the above
19. In a semiconductor, current conduction is
due ........
(i) only to holes
(ii) only to free electrons
(iii) to holes and free electrons
(iv) none of the above
20. The random motion of holes and free electrons
due to thermal agitation is called ........
(i) diffusion (ii) pressure
(iii) ionisation (iv) none of the above
21. A forward biased pn junction has a resistance
of the ........
(i) order of Ω (ii) order of kΩ

(iii) order of MΩ (iv) none of the above

22. The battery connections required to forward
bias a pn junction are ........
(i) +ve terminal to p and −ve terminal to n

(ii) −ve terminal to p and +ve terminal to n

(iii) −ve terminal to p and −ve terminal to n

(iv) none of the above
23. The barrier voltage at a pn junction for germanium
is about ........
(i) 3.5 V (ii) 3V
(iii) zero (iv) 0.3 V
24. In the depletion region of a pn junction, there
is a shortage of ..........
(i) acceptor ions (ii) holes and electrons
(iii) donor ions (iv) none of the above
25. A reverse biased pn junction has ........
(i) very narrow depletion layer
(ii) almost no current
(iii) very low resistance
(iv) large current flow
26. A pn junction acts as a ........
(i) controlled switch
(ii) bidirectional switch
(iii) unidirectional switch
(iv) none of the above
27. A reverse biased pn junction has resistance
of the........
(i) order of Ω (ii) order of kΩ

(iii) order of MΩ (iv) none of the above

28. The leakage current across a pn junction is
due to ........
(i) minority carriers
(ii) majority carriers
(iii) junction capacitance
(iv) none of the above
29. When the temperature of an extrinsic semiconductor
is increased, the pronounced
effect is on ........
(i) junction capacitance
(ii) minority carriers
(iii) majority carriers
(iv) none of the above
30. With forward bias to a pn junction, the width
of depletion layer ........
(i) decreases (ii) increases
(iii) remains the same
(iv) none of the above
31. The leakage current in a pn junction is of
the order of ........
(i) A (ii) mA
(iii) kA (iv) μA
32. In an intrinsic semiconductor, the number of
free electrons ........
(i) equals the number of holes
(ii) is greater than the number of holes
(iii) is less than the number of holes
(iv) none of the above
33. At room temperature, an intrinsic semiconductor
has ........
(i) many holes only
(ii) a few free electrons and holes
(iii) many free electrons only
(iv) no holes or free electrons
34. At absolute temperature, an intrinsic semiconductor
has ........
(i) a few free electrons
(ii) many holes
(iii) many free electrons
(iv) no holes or free electrons
35. At room temperature, an intrinsic silicon
crystal acts approximately as ........
(i) a battery
(ii) a conductor
(iii) an insulator
(iv) a piece of copper wire

Answers to Multiple-Choice Questions

1. (i) 2. (iii) 3. (ii) 4. (iv) 5. (ii)
6. (ii) 7. (ii) 8. (iii) 9. (iv) 10. (i)
11. (ii) 12. (iii) 13. (iv) 14. (i) 15. (ii)
16. (ii) 17. (iii) 18. (ii) 19. (iii) 20. (i)
21. (i) 22. (i) 23. (iv) 24. (ii) 25. (ii)
26. (iii) 27. (iii) 28. (i) 29. (ii) 30. (i)
31. (iv) 32. (i) 33. (ii) 34. (iv) 35. (iii)