Re: brightness vrs. power

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

I'm coming to this late as usual, but I don't think one needs to make
any assumptions about the Ohmic nature of a bulb to use bulbs in a
conceptual exercise about circuits.  If the temperature is allowed to
vary freely, then clearly they are non-Ohmic and grossly so.  But that
does not obscure their use as students try to understand that batteries
are not constant current sources  when they think otherwise, etc.

cheers,

joe

On Wed, 3
May 2000, David Strasburger-fac wrote:

> PHYS-L@lists.nau.edu writes:
> > > Radiant energy depends on temperature of a filament. For instance when
> > two
> > > similar bulbs are connected in series the net current is (approximately)
> > > halved. The power dissipated in both bulbs is reduced by factor 1/4.
> >
> > I don't know how you calculated this, but it is incorrect. Light bulbs
> > do not obey Ohm's law. They are extremely nonlinear.
>
> This may be true, but I saw a demonstration about three summers ago in
> which the instructor broke the glass on a household bulb and immersed the
> filament in a bath of water with an electric stirrer to keep the
> temperature as uniform as possible.  He varied voltage and measured
> current -- I have to say the relationship looked awfully linear to me.
>
> David