RESISTANCE CHANGES

Radio Record, Volume I, Issue 27, 20 January 1928, Page 15

RESISTANCE CHANGES

TEMPERATURE EFFECTS. Many listeners cannot understand why a certain length of wire possessing a known value of resistance will show a variation while current is flowing through it. To comprehend this phenomena, certain actions must he visualised by the interested fan. Tirst, the, formation of molecules results in the wire possessing a certain value of resistance per inch, foot, or mile of wire, whichever dimensions suits the fan If the molecular structure of the wire is altered, the resistance for that inch, foot or mile of wire is changed. The more the structure is varied, the greater the change in resistance. When current is caused to pass through wire the action of the current is to heat the wire, the heat generated being dependant upon the amount of current flow The action of the current not oily heats the wire, but in heating it changes its molecular formation, with the result that the resistance changes. Molecular Structure. It must be understood, however, that the molecnlar structure is not always altered by the heat generated in the wire. That is, the elements comprising the wire may have such molecular formation that within certain limits of heat, these formations will not change appreciably, with the result that the resistance of the wire dees not change with increase in temperature, Such a wire is said to possess negligible temperature coefficient and the resistance remains practically constant over at. certain range of applied watts Such resistances are best suited in battery. eliminators and c¢lectrificd receivers where constant resistance is mecessary under various loads.