171. The drift of a hole in a semiconductor is brought by –
(a) The vacancy being filled by a free electron
(b) The vacancy being filled by an ion
(c) The vacancy being filled by a valence electron from a neighbouring atom
(d) The movement of an atom in the solid
172. A substance has an electron concentration of 8 x 106 per m3 and a hole concentration of 2 x 1012 per m3. The substance is –
(a) An intrinsic semiconductor
(b) A n- type semiconductor
(c) A p- type semiconductor
(d) An insulator
173. When the conductivity of semiconductor is only due to the breaking of the covalent bands, the semiconductor is –
(a) An intrinsic semiconductor
(b) A p- type semiconductor
(c) A n- type semiconductor
(d) an extrinsic semiconductor
174. In Intrinsic semi conductor the valence and conduction bands –
(a) Overlap with each other
(b) Are separated by an energy gap of about 1 eV
(c) Are separated by an energy gap of about 10 eV
(d) Are separated by an energy gap about 0.001 eV
175. The energy band gap of silicon is –
(a) 0.72 eV
(b) 1.1 eV
(c) 6 eV
(d) Between 0.72 eV to 1.1 eV
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