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Electrical Engineering Objective Questions { Material And Components }

78.  At absolute zero, all the valence electrons in an intrinsic semiconductor are
A. in the conduction band
B. in the forbidden band
C. in the valence band
D. reduced to zero in number
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79. Germanium
A. can not be purified by zone refining method
B. is usualy purified by the floating zone method
C. is more easily purified than silicon
D. has melting temperature higher than silicon
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80. In a semiconductor, rate of diffusion of charge carriers
A. depends on the concentration gradient and the mobility
B. depends on the concentration gradient alone
C. depends on the mobility alone
D. is independent of concentration gradient and the mobility
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81. Adjacent atoms in the crystalline structure of a semiconductor like germanium form
A. ionic bands
B. metallic bands
C. molecular bands
D. covalent bands
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82. When a pure semiconductor is heated
A. its resistance increases
B. its resistance decreases
C. its atomic structure changes
D. it becomes metal
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83. Valence electrons are
A. found in the nucleus
B. the inner core electrons of an atom
C. the outer orbit electrons
D. always free electrons
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84. Pure semiconductors are poor conductor because
A. they have no valence electrons
B. all valence electrons are in electron pairs
C. they have a number of holes
D. there are fewer electrons than protons
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