21.4. Measurement Techniques: Electrical
21.4.1. Resistance Thermometers
All metals are electrical conductors that, at all but very low temperatures, offer resistance to the passage of electric current. The electrical resistance exhibited by a conductor is measured in ohms. The proportional relationship of electrical current and potential difference is given by Ohm's law:
where
R is resistance in ohms,
E is potential difference in volts, and
I is current in amperes. Different metals show widely different resistivities. The resistance of a conductor is proportional to its length and inversely proportional to its cross-sectional area, that is, ...
(21.10)
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