161. If a small amount of phosphorus is added to silicon :
(a) The conductivity decreases
(b) The silicon will be a p-type semiconductor
(c) The phosphorus becomes an acceptor impurity
(d) There will be more free electrons than holes in the semiconductor
162. The electrical resistivity of :
(a) Intrinsic semiconductor decreases with decreases of temperature
(b) Intrinsic semiconductor decreases with increases of temperature
(c) Metals is independent of temperature at high temperature
(d) Metals decreases with increasing temperature
163. A piece of silicon or germanium at 0˚C is :
(a) An insulator
(b) A semiconductor
(c) A conductor
(d) A superconductor
164. A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of :
(a) Each of them increases
(b) Each of them decreases
(c) Copper increases and germanium decreases
(d) Copper increases and germanium increase
165. The electrical conductivity of a pure silicon or germanium sample can be increased by :
(a) Increasing the temperature Doping it with acceptor impurity
(b) Doping it with acceptor impurity
(c) Doping it with donor impurity
(d) Shining ultraviolet light on it
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