Date: Fri Nov 2 14:14:42 2007

Author: Bernard Cleyet

Subject: Re: Labs on Magnetic Materials

Post:
Urs' expt. is the exact one (including successively switching resistors
is the correct order, etc.) that I did back in about 1957. The only
difference is we used a precision ballistic galvanometer and the coils
are solenoids, thereby, various materials may be measured. The primary
(H) is long and the sec. (B) is short wound on the primary centred
solenoid switches and resistors mounted on a bread board.

bc has a similar app, hanging on one of our hall's walls.


Urs Lauterburg wrote:

> Mary Ann,
>
> We have a lab here which seems to be similar to the one written about
> in the AJP article. We make our students measure the magnetizing curve
> of two different toroid cores, one is what we call glowed (heat
> treated) and the other one is not. Both cores show different tapes of
> magnetizing curves and hysteresis. Both toroids have secondary and
> primary windings and the lab's aim is to have the students perform
> accurate and well controlled measurements of the integrated signals
> off the secondary windings as a response to changes of the DC current
> through the primary windings. The primary current comes from a DC
> power supply and is changed by switching between different resistors
> in series with the primary input circuit. The secondary response is
> integrated by a stand-alone, self-made precision integrator. A digital
> oscilloscope is triggered with the secondary response and measures the
> integrator output for each resistor (current) change. All points have
> to be measured in a full sequence. If a group makes just one mistake,
> they have to demagnetize the toroid core and start all over again.
>
> If they do it right, and a great part is about measurement technique,
> they get the initial magnetizing as well as one full cycle of the
> Hysteresis curve with the top end precisely closing the cycle at the
> positive magnetizing saturation. From the measurements and the given
> parameters like number of windings, integrator data etc. the students
> can determine all relevant parameters of the characteristic hysteresis
> loop for the two different core materials.
>
> It's a basic experiment which represents some very important
> macroscopic aspects of magnetism and the students learn a lot about
> properly performing a clean series of measurements with a DSO.
>
> I hope my explanation will be somehow useful for you
>
> Urs
>
> Urs Lauterburg
> Physics demonstrator
> Physikalisches Institut
> University of Bern
> Switzerland
>
>> Hey, y'all.
>>
>> Does anyone do an intro or intermediate E&M lab on magnetic materials?
>>
>> In particular, do any of you use the Tel-Atomic Magnetic Bubble
>> Apparatus (http://www.telatomic.com/mba.html) for a quantitative
>> experiment? Two articles from the early 1980's, AJP 48(1), 59 (1980)
>> and TPT 20,330 (1982) describe an experiment, but I'm interested in
>> insights to how it works in practice.
>>
>> I also came across another AJP article (66(5), 449 (1998)) that
>> describes mapping the magnetization curve of a toroidal sample of
>> ferromagnetic material. The sample is wrapped with two windings. One
>> winding is connected to a current source, producing a magnetic field,
>> and the other winding is connected to an inductance meter. The
>> inductance is proportional to the magnetic permeability. Does this
>> sound like a familiar experiment to anyone? Thoughts?
>>
>> Are there any other experiments, either quantitative or qualitative
>> you do on this topic that you'd recommend?
>>
>> Thanks!
>> Mary Ann
>>
>> ***********************************************
>> Mary Ann Hickman Klassen
>> Lecturer
>> Dept. of Physics & Astronomy
>> Swarthmore College
>> 500 College Ave.
>> Swarthmore, PA 19081
>> phone: 610-328-8384 fax: 610-328-7895
>> **********************************************
>
>
>
>

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