There is a significant current surge when you first switch on a filament lamp .
what's the theoretical model of this phenomenon ?
I assume that there is a huge different between ac & dc in this case .
some one told me that i should get help from faradic , or this formula : L( di / dt )
Please help me out !
I'm so confused
2007-02-23 01:03:30 · 3 answers · asked by Myself 1 in Science & Mathematics ➔ Engineering
Do a search on "Temperature coefficient of resistance"
2007-02-23 01:17:00 · answer #1 · answered by lunchtime_browser 7 · 1⤊ 0⤋
The resistance of a tungsten filament increases with temperature.
Before switching the lamp on the filament is cold and has a low resistance. The initial current will therefore be relatively high.
(This is why a domestic light bulb usually fails at switch-on.)
The filament heats up rapidly (a few tens of milliseconds), the resistance increases and the current diminishes.
It makes no difference whether the filament is supplied with d.c. or a.c.
2007-02-23 10:09:48 · answer #2 · answered by dmb06851 7 · 0⤊ 0⤋
the main reason of the present surge while first switched on is by way of the fact the Tungsten filament is chilly. while tungsten is chilly it has a low resistance, and consequently the present is severe - by using fact the filament immediately warms up, the resistance will boost without postpone, reducing the present point. If I = V / R ----- you will locate that if R is small, V does not replace and subsequently I is huge. As R increses I will become smaller. it is the main reason a bulb will blow once you first change it on.....
2016-12-17 17:01:07 · answer #3 · answered by Anonymous · 0⤊ 0⤋