Date: Tue, 25 Oct 2011 18:50:31

Author: Steve Wonnell

Subject: Re: Image Current Demo

Post:


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Hi Jerry,

Yes, and it's helpful for visualizing the fields, too.

I was thinking, it might be possible to develop this phenomenon into a =
"image current" demo after all.

Imagine poking a hole through one of the Leybold magnet arrays, and =
running the wire through the hole, so as to show the magnetic field =
produced by the current running through the wire. Make two of these.

WIth one of these, place it against a soft magnetic material. Run =
current through the coil to to produce a field that the magnet array =
will display. The array of magnets will arrange itself so as to =
represent the field due to the wire plus that due to induced magnetic =
dipoles in the soft magnetic material. Have several different magnetic =
materials of different magnetic permeability available.

WIth the other, position a second wire parallel to the first, as far =
from the edge of the Leybold array as is the first wire (so the spacing =
between the two wires is the width of the array). Connect this wire to =
a power supply as well; call the wire the "image wire." When the =
current through this image wire is equal to (u-1)/(u+1) where u is the =
relative permeability of the magnetic material, then the array of =
magnets should look identical to that of the first situation.

In this way, this could really be a demo of "image currents."

The Leybold magnet array that I mention is =
http://www.ld-didactic.de/phk/a.asp?a=3D56061&L=3D2

Steve


On Oct 25, 2011, at 5:18 PM, Zani, Gerald wrote:

> Steve,
>=20
> You stated very clearly what is indeed my understanding.
>=20
> Image charge and inage current is an imaginary, mathematical idea used =
to build up, or construct a good method for problem solving.
>=20
> No?=20
>=20
>=20
> - Jerry Z.
>=20
> On Tue, Oct 25, 2011 at 4:55 PM, Steve Wonnell =
wrote:
> Hi Jerry,
>=20
> I don't think it really demonstrates the image current. I think it =
demonstrates the attraction between an electric current and a =
ferromagnetic object, analogously to how an electric charge is attracted =
to a metal plate by electrostatic induction.
>=20
> If anyone has tried to measure the magnitude of the image current, it =
should be zero. It's not really there. It's just a mathematical =
viewpoint.
>=20
> Steve
>=20
>=20
>=20
>=20
> On Oct 25, 2011, at 4:34 PM, Jerry DiMarco wrote:
>=20
> > Following along with Steve's thought, if the effect is on =
magnetic dipoles in a ferromagnetic material, why is this called an =
image current demo?
> >
> > =
Jerry D
> >
> >
> > At 10/25/2011 03:56 PM, you wrote:
> >> Hummm, George, come to think of it, is this effect really any =
different from, say, the force that makes an iron core retract into a =
solenoid when the current is turned on? -- Steve
> >>
> >>
> >> You know how if you have an iron core for a solenoid, the core is =
pulled into the solenoid when current is run through
> >> On Oct 25, 2011, at 2:15 PM, George Herold wrote:
> >>
> >>> Just a though on another way to do this. If you have a nice coil =
for making B-fields (I'm thinking of 1/2 of a Helmholtz pair.) And a =
magnetometer... perhaps a simple hall probe. Then you can put a current =
through the coil and make a B-field. Measure the size with the hall =
probe. Now bring a large piece of iron near to the coil.. (from the =
side opposite side of the hall probe) the field should increase. (Of =
course ya gotta make sure the iron isn't magnetized already.)
> >>>
> >>> George
> >
>=20
> **********************************************
> Steven K. Wonnell, Ph.D.
> Manager, Physics Instructional Resources
> Department of Physics and Astronomy
> The Johns Hopkins University
> 3400 N. Charles Street
> Room 534 Bloomberg Center
> Baltimore, MD 21218
> Phone: 410-516-5468
> E-Mail: wonnell@pha.jhu.edu
> **********************************************
>=20
>=20
>=20
>=20
>=20
>=20
>=20
> --=20
> Gerald Zani
> Demonstration Manager
> Physics
> Brown University
> (401) 863-3964
>=20

**********************************************
Steven K. Wonnell, Ph.D.
Manager, Physics Instructional Resources
Department of Physics and Astronomy
The Johns Hopkins University
3400 N. Charles Street
Room 534 Bloomberg Center
Baltimore, MD 21218
Phone: 410-516-5468
E-Mail: wonnell@pha.jhu.edu
**********************************************




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Hi =
Jerry,Yes, and it's helpful for visualizing the =
fields, too.I was thinking, it might be =
possible to develop this phenomenon into a "image current" demo after =
all.Imagine poking a hole through one of the =
Leybold magnet arrays, and running the wire through the hole, so as to =
show the magnetic field produced by the current running through the =
wire. Make two of these.WIth one of these, =
place it against a soft magnetic material. Run current =
through the coil to to produce a field that the magnet array will =
display. The array of magnets will arrange itself so as to =
represent the field due to the wire plus that due to induced magnetic =
dipoles in the soft magnetic material. Have several different =
magnetic materials of different magnetic permeability =
available.WIth the other, position a second =
wire parallel to the first, as far from the edge of the Leybold array as =
is the first wire (so the spacing between the two wires is the width of =
the array). Connect this wire to a power supply as well; call the =
wire the "image wire." When the current through this image wire is =
equal to (u-1)/(u+1) where u is the relative permeability of the =
magnetic material, then the array of magnets should look identical to =
that of the first situation.In this way, this =
could really be a demo of "image currents."The =
Leybold magnet array that I mention is http://ww=
w.ld-didactic.de/phk/a.asp?a=3D56061&L=3D2SteveOn Oct 25, =
2011, at 5:18 PM, Zani, Gerald wrote:Steve,You stated very clearly what is =
indeed my understanding.Image charge and inage =
current is an imaginary, mathematical idea used to build up, or =
construct a good method for problem solving.

No? - Jerry =
Z.On Tue, Oct 25, 2011 at 4:55 =
PM, Steve Wonnell =
wrote:

Hi Jerry,

I don't think it really demonstrates the image current. I think it =
demonstrates the attraction between an electric current and a =
ferromagnetic object, analogously to how an electric charge is attracted =
to a metal plate by electrostatic induction.



If anyone has tried to measure the magnitude of the image current, it =
should be zero. It's not really there. It's just a =
mathematical viewpoint.

Steve




On Oct 25, 2011, at 4:34 PM, Jerry DiMarco wrote:

> Following along with Steve's thought, if the effect =
is on magnetic dipoles in a ferromagnetic material, why is this called =
an image current demo?
>
> =
=
=
=
Jerry D
>
>
> At 10/25/2011 03:56 PM, you wrote:
>> Hummm, George, come to think of it, is this effect really any =
different from, say, the force that makes an iron core retract into a =
solenoid when the current is turned on? -- Steve
>>
>>
>> You know how if you have an iron core for a solenoid, the core =
is pulled into the solenoid when current is run through
>> On Oct 25, 2011, at 2:15 PM, George Herold wrote:
>>
>>> Just a though on another way to do this. If you have =
a nice coil for making B-fields (I'm thinking of 1/2 of a Helmholtz =
pair.) And a magnetometer... perhaps a simple hall probe. =
Then you can put a current through the coil and make a B-field. =
Measure the size with the hall probe. Now bring a large =
piece of iron near to the coil.. (from the side opposite side of the =
hall probe) the field should increase. (Of course ya gotta make =
sure the iron isn't magnetized already.)


>>>
>>> George
>

**********************************************
Steven K. Wonnell, Ph.D.
Manager, Physics Instructional Resources
Department of Physics and Astronomy
The Johns Hopkins University
3400 N. Charles Street
Room 534 Bloomberg Center
Baltimore, MD 21218
Phone: 410-516-5468
E-Mail: wonnell@pha.jhu.edu
**********************************************




-- Gerald =
ZaniDemonstration ManagerPhysicsBrown University(401) =
863-3964


wonnell@pha.jhu.edu****=
******************************************

=

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