Interesting non-linear effects

Andre Kesteloot andre.kesteloot at
Fri Nov 9 22:28:34 CST 2012

On 11/9/2012 14:44 PM, Karl W4KRL wrote:
> [...]
> */The low cold resistance of a tungsten filament results in a marked 
> inrush of current when the lamp is lighted. Though the current and the 
> power consumption rise momentarily to values far above those of steady 
> operation, the candlepower does not "overshoot" but rises gradually to 
> its steady value. The relative magnitude of the initial surge of 
> current and power depends to some extent upon the resistance and in 
> greater degree upon the inductance of the circuit in which the lamp is 
> connected. If the lamp is operated in an a-c circuit, the amount of 
> the surge depends also upon the phase of the voltage wave at which the 
> switch is closed. Oscillographic records of the starting of a 300-W, 
> 120-V lamp, having hot-to-cold resistance ratio 15.5, showed a maximum 
> surge crest current of 47 A in a circuit having 0.1 Ohm resistance and 
> 0.04 Ohm reactance at 60 c. ..."/*
  Could we measure the real resistance of the filament by  --for 
instance--  slowly heating up the light bulb in an oil bath , waiting 
for the temperature to eventually stabilize ?
Then we would have all the time to measure the change of R vs. t, as 
opposed to trying the record the transient at the point of turning ON 
the bulb?
André N4ICK
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