61. Purification of silicon is difficult because of :
(a) Its high surface tension
(b) Its crystalline nature
(c) Its high melting point
(d) Its high resistivity
62. Excess majority carriers are the carriers which are :
(a) Equal to the number of hole concentration
(b) In excess of the equilibrium number
(c) Minority carriers in P-type semiconductor
(d) Thermally generated
63. A plasma is a :
(a) Collection of electrons, positive and negative ions only
(b) Collection of electrons and positive ions only
(c) Collection of neutral atoms and molecules only
(d) Collection of electrons, positive and negative ions, neutral atoms and molecules
64. Hole in a lattice is defined as :
(a) Free proton
(b) Free neutron
(c) Acceptor ion
(d) Vacancy created by removal of electron from covalent bond.
65. In germanium, when atoms are held together by the sharing of valence electrons :
(a) Each shared atom leaves a hole
(b) Valence electrons are free to move away from the nucleus
(c) They form reversible covalent bonds
(d) They form irreversible covalent bonds
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