Date: Thu Nov 1 16:12:26 2007

Author: --- mklasse1

Subject: Re: Labs on Magnetic Materials


On Nov 1, 2007, at 12:33 AM, Bernard Cleyet wrote:

> That doesn't make sense; what kinda inductance meter?

According to the Borin & Balfa (AJP 66(5), 449) paper, they used a
Wavetek DM27XT digital multimeter operating at 1 kHz to measure
The magnetic field H was provided by a DC power supply.

Reading the paper more closely, it looks like they first plot
permeability as a function of H. (Mu being proportional to L.)
Then, taking mu to be the derivative of B with respect to H, they
numerically integrated the mu vs. H data to calculate B.
I think that must be where their experiment differs from the classic

> The experiment you describe is similar to ones done a century ago.
> I have the apparatus similar to what we used in the fifties. The
> detector (second winding) was a ballistic galvanometer (it
> integrates). Now one may use a 'scope. However, the output must
> be integrated (use a cap.) The input magnetization (H) is prop. to
> the current, so the X looks at the potential dropped by a
> resistor. The Y (B) across the cap. I think this was described
> in a TPT. Certainly in some AJP articles. Just about any two
> coils w/ anything in them can be used. For a quick demo. I used an
> ordinary transformer. (audio or filament?) input th line using a
> variable auto xformer (Variac). A sig. gen. and power amp. for
> other freaks.
Thanks, I'll look farther back in the journal archives.

--Mary Ann

Mary Ann Hickman Klassen
Dept. of Physics & Astronomy
Swarthmore College
500 College Ave.
Swarthmore, PA 19081
phone: 610-328-8384 fax: 610-328-7895