85. Hole in a lattice is defined as
A. free proton
B. free neutron
C. vacancy created by removal of electron from covalent band
D. acceptor ion

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86. In a pure semiconductor, electric current is due to
A. holes alone
B. electrons alone
C. both holes and electrons
D. valence electrons alone

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87. Forbidden energy gap between valence band and conduction band is least in the case of
A. mica
B. pure silicon
C. pure germanium
D. impure silicon

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88.  Temperature coefficient of resistance in a pure semiconductor is
A. zero
B. positive
C. negative
D. dependent on size of specimen

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89. Donor impurity atom in a semiconductor result in new
A. wide energy band
B. narrow energy band
C. discrete energy level just below conduction level
D. discrete energy level just above valence level

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90. Acceptor impurity atoms in a semiconductor result in new
A. wide energy band
B. narrow energy band
C. discrete energy level just below conduction level
D. discrete energy level just above valence level

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91. In Ge or si, medium doping corresponds to impurity of the following order
A. 1 part in 108
B. 1 part in 106
C. 1 part in 105
D. 1 part in 104

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