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:
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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, ...

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