Re: Ohm's Law

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Hi,

      Halogen bulbs are a bit odd.  The idea of
using a very reactive gas in the bulb initially
made not sense to me.  Then I learned that the
halogen gas will bond with the tungsten after it
evaporates from the filament and the tungsten
which has been deposited on the glass.  But when a
tungsten halide bumps into the very hot filament
it dissociates, depositing the scavenged tungsten
back on the filament.  I guess at below rated
voltage the halogens eat the filament.

Thanks
Roger Haar








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David Bowman wrote:
> Regarding Mark's comment of 07 MAR 03:
>
> > The variation is certainly noticeable when one uses the Pasco "light
> > sensor" with a datalogging interface. We were using a halogen lamp on 12V
> > ac as the source in a polarisation experiment some time back. The
> > measurements drifted up and down in a regular way that turned out to be a
> > slow beat between the 100 Hz of the mains and the sampling frequency, not
> > quite 20 Hz. We learnt that we had to use well-smoothed DC. We also learnt,
> > btw, that halogen lamps die very quickly when run at below their rated voltage.