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The temperature coefficient of resistivity a is given by
Where p is the resistivity at the temperature T. Equation (25.6) then follows if a is assumed constant and much smaller than (T – T0)-1
(a) If a is not constant but is given by a = -n/T, where T is the Kelvin temperature and n is a constant, show that the resistivity is given by p = a/Tn, where a is a constant.
(b) From Fig, you can see that such a relationship might he used as a rough approximation for a semiconductor. Using the values of p and a for carbon from Tables 25.1 and 25.2, determine a and n. (In Table 25.1. assume that room temperature" means 293 K).
(c) Using your result from part (b). Determine the resistivity of carbon at -196°C and 300°C. (Remember to express T in Kelvins.) |
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