Date: Fri Oct 30 11:54:51 2009 ** **Back to Contents ** ------------------------------------------------------------------------ **

Author: bennett bennett

Subject: Re: Weber-Kohlrausch experiment

Post:

Many decades ago, I was shown a dimensional derivation that showed
the speed of light to equal thirty ohms.

I suspect this is the samething

On 10/30/09, Wolfgang Rueckner wrote:
> thank you Cliff ... this is what I had in mind -- Wolfgang
>
>
>
>
> On Oct 30, 2009, at 9:52 AM, cbettis@unlserve.unl.edu wrote:
>
>
> > Wolfgang,
> >
> > This is what I did:
> >
> > 1. I showed a demonstration galvanometer, pointing out we need to
> calibrate it to measure current.
> >
> > 2. I showed a ballistic galvanometer and how the critical damping would
> allow us to integrate a current pulse and give us a way of measuring charge.
> >
> > 3. I used a current balance to calibrate a galvanometer (assuming
> standards for mass, force and length).
> >
> > 4. I used a flip coil, Helmholtz coils and the calibrated galvanometer to
> calibrate my ballistic galvanometer.
> >
> > 5. I did the Joule experiment to calibrate a voltmeter (heating a resistor
> with a known current lets you calibrate the resistor, hence a voltmeter).
> >
> > 6. Using the calibrated voltmeter and series resistors I measured the EMF
> of a 500 V battery.
> >
> > 7. I used the battery to charge a parallel plate capacitor of known area
> and separation. I then discharged that capacitor through the calibrated
> ballistic galvanometer to measure the stored charge.
> >
> > 8. Using the geometry of the capacitor and its stored charge at a
> particular voltage, I calculated the electrical permittivity of a vacuum (I
> got 1 x 10**-11 C**2/N M**2 with my particular equipment).
> >
> > 9. Using the electrical permittivity and the defined magnetic permeability
> of the vacuum, I calculated c.
> >
> > Cliff
> >
> > Quoting Wolfgang Rueckner :
> >
> >
> > > Cliff -- that would be wonderful. It is measuring c the hard way, but
> > > that's not the point. The historical point is that c could be
> > > determined from only electric and magnetic quantities. -- Wolfgang
> > >
> > >
> > >
> > >
> > > On Oct 29, 2009, at 3:52 PM, cbettis@unlserve.unl.edu wrote:
> > >
> > >
> > > > Wolfgang,
> > > >
> > > > I went through this set of experiments for a colloquium once. I
> called it "Measuring c the hard way." I went from first principles to
> calibrate volt and ammeters using a current balance and thermometry and
> finally the parallel plate capacitor and ballistic galvanometer. It all
> worked well but gave me an appreciation of how far we've come. After all,
> we don't measure c anymore: it's a definition. If I look around maybe I
> can find my notes (this was a couple of decades ago, I think.)
> > > >
> > > > Cliff
> > > >
> > > > Quoting Wolfgang Rueckner :
> > > >
> > > >
> > > > > I'd like to attempt the 1856 experiment of Wilhelm Weber & Rudolph
> > > > > Kohlrausch in which they unified electric and magnetic phenomena and
> > > > > made the connection with light. This is the work that enabled
> Maxwell
> > > > > to predict the propagation velocity of electromagnetic waves. To
> > > > > potentially save myself time in "re-inventing the wheel," I am
> curious
> > > > > if anyone out there has already done this and can share tips on the
> > > > > do's and don'ts. Or, if you know of a published paper on this (in
> one
> > > > > of the educational journals), references are appreciated too. --
> > > > > Wolfgang
> > > > >
> > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
> >
>
>

--
Clarence Bennett
Oakland University
Dept. of Physics, (retired)
111 Hannah
Rochester MI 48309
248 370 3418

From tap-l-owner@lists.ncsu.edu Fri Oct 30 11:54:51 2009
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