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The transistor are usually made of
(a) metal oxides with high temperature coefficient of
resistivity
(b) metals with high temperature coefficient of resistivity
(c) metals with low temperature coefficient of resistivity
(d) semiconducting materials having low temperature
coefficient of resistivity
Answer:(a) metal oxides with high temperature coefficient of resistivity.
Thermistors are substances whose resistance changes with the change in temperature. The resistance of the material with high temperature coefficient of resistivity changes more rapidly, than that of other materials having low coefficient of resistivity.
Formula used:
From the above expression we can imply that the materials with high temperature coefficient of resistivity, the resistance of such materials will change with even small changes in the temperature. Metal oxides have a very high temperature coefficient of resistivity than that of their respective metals. Hence thermistors are mostly made of metal oxides.
It is to be noted that metal oxides have very less electrons in their conduction band. And hence when the temperature increases there is more effective Brownian motion of these electrons. As the Brownian motion increases the electrons hit each other with smaller relation time. Hence the flow of electrons across the material is restricted thereby decreasing the flow of current in the circuit. It is also to be noted that all metals have the temperature coefficient of resistivity as positive while the semiconducting materials have temperature coefficient of resistivity as negative.
Transistor
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