Abstract
The leads of a tungsten filament in vacuum cool the ends of the filament and so affect the voltage, candle power, electron emission and other properties of the filament. For long filaments, where there is a central portion at a uniform temperature Tm, the temperature distribution near the lead is derived. A method for determining T0, the temperature of the lead-filament junction, is given. Tables and formulas are presented which allow ready calculation of the effect of the leads on the properties of any long tungsten filament for which the current and diameter are known. From the more general results it has been found that the decrease in voltage due to the cooling of one lead may be represented by δV = 0.154 (Tm/1000)–0.081 (T0/1000)–2.1.10-8T0Tm–0.056. There is an extension of the theory to cover the cases of filaments in gases, filaments of other materials, etc.
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