1. In an intrinsic semiconductor, the Fermi level

a. Lies at the center of forbidden energy gap.

b. Is near the conduction band.

c. Is near the valence band.

d. May be anywhere in the forbidden energy gap.

Ans: a

2. The ratio of impurity atoms to intrinsic semiconductor atoms in an extrinsic semiconductor is about.

a. 1:10  b. 1:103   c. 1:105   d. 1:108

Ans: d

3. In a P type material the Fermi level is 0.3 eV above the valence band. The concentration of accepter atoms is increased. The new position of Fermi level is likely to be

a. 0.5 eV above the valence band.

b. 0.2 eV above the valence band.

c. Below the valence band.

d. None of the above

Ans: b

4. Most commonly used semiconductor material is

a. Silicon

b. Germanium

c. Mixture of silicon and germanium

d. None of the above.

Ans: a

5. At room temperature a semiconductor material is

a. Perfect insulator

b. Conductor

c. Slightly conducting

d. Any one of the above.

Ans: c

6. For silicon, the energy gap at 300 K is

a. 1.1 W  b. 1.1 J s c. 1.1 eV  d. None of these

Ans: c

7. The forbidden gap for germanium is,

a. 0.12 eV  b. 0.72 eV  c. 7.2 eV  d. None of these

ans: c

8. The process of adding impurities to a pure semiconductor is called

a. Mixing b. Doping c. Diffusing d. None of the above

Ans: b

9. The pentavalent impurities like antimony, arsenic, bismuth and phosphorus, added to intrinsic semiconductors are called

a. Acceptor or P-type impurities

b. Donor or P-type impurities

c. Acceptor or N-type impurities

d. Donor or N-type impurities

Ans: d

 10. Impurities like boron, aluminum, gallium or indium are added to intrinsic semiconductor to form

a. N-type doped semiconductor

b. P-type doped semiconductor

c. A junction diode

d. All of these

Ans: b

11. In a N-type semiconductor, the position of Fermi-level

a. Is lower than the center of energy gap

b. Is at the center of energy gap

c. Is higher than the center of energy gap

d. Can be any where

Ans: c

 12. The mobility of electrons in a material is expressed in unit of:

a. V/s        b. m2/V-s   c. m2/s            d. J/K

Ans: b

13. In a metal

a. The electrical conduction is by electrons and holes

b. The conductivity decreases with the rise in temperature

c. The conduction band is empty

d. None of the above

Ans: b

14. The energy gap in a semiconductor

a. Increases with temperature

b. Does not change with temperature

c. Decreases with temperature

d. Is zero

Ans:  c

 15. Two initially identical samples A and B of pure germanium are doped with donors to concentrations of 1×1020 and 3x1020respectively. If the hole concentration in A is 9×1012, then the hole concentration in B at the same temperature will be

a. 3×1012 m-3 b. 7×1012 m-3

c. 11×1012 m-3 d. 27×1012 m-3

Ans: a

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