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Friday, 26 July 2019

Classification of High Resistivity Materials based on uses

Requirements of High Resistivity Conducting Materials :

Some of the essential requirements of high resistivity conducting materials are :

(a) High specific resistance.
(b) Ductility and malleability.
(c) Should not be brittle.
(d) Should have low temperature co-efficient of resistance.
(e) Should have high melting point.
(f) Should not get easily oxidised on heating.
(g) Should be able to dissipate much heat per unit volume.

Classification of High Resistivity Materials based on uses:

High resistivity conducting materials are mostly alloys of different metals. Manganin, Eureka, and Nichrome are examples for this type of material. Based on their practical use they can be divided into three groups.

(a) The first group consists of materials used in precisions electrical measuring instruments, standard resistances and resistance boxes.

(b) The second group consists of materials used for all types of rheostats and similar control devices.

(c) The third group consists of the materials used for high temperature heating elements, loading rheostats etc.

The first group of materials should have least temperature co-efficient of resistivity and good stability in resistance value over long period of time. The thermo electro motive force of this material with copper should be minimum because the e.m.f. affect the accuracy of measurement. The most important material of this group is Manganin.

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