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## possible to draw static magnetic field lines on a bar magnet in 3D post and replies

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possible to draw static magnetic field lines on a bar magnet in 3D - Aug 3, 2012 at 12:46PM

lookang
175 Posts

is it possible to draw static magnetic field lines on a bar magnet in 3D? i looked at examples in EJS, E:\workspace\source\ModelingScience\Ch03_Basics\DipolePotential.xml it resembled the magnetic field lines of a magnet bar. is it possible to create a 3D version of this? it would be useful to many physics EJS users trying to draw "unchanging" field lines without the need to ODE. for your consideration :)

or maybe my question should be can share a EJS example of an 3D magnetic lines of a bar magnet?

thanks!

Post edited August 3, 2012 at 12:39 PM EST.

Post edited August 3, 2012 at 12:41 PM EST.

Post edited August 3, 2012 at 12:41 PM EST.

Post edited August 3, 2012 at 12:42 PM EST.

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### Replies to possible to draw static magnetic field lines on a bar magnet in 3D

Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 03 2012 4:17PM
Wolfgang
103 Posts

EJS 3D objects can indeed be used to plot field lines.  There are two ways to do this:

1) Use the analytic formula for a dipole to generate a sequence of (x,y,z) points for a Trail3D Element.
2) Solve the ODE for the field line starting at some initial point (x0,y0,z0) and store the solution in a Trail3D.

In general, I think field vectors provide a better representation than field lines. See the following E&M programs for this representation:

Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 04 2012 9:47AM

lookang
175 Posts

quote:
1) Use the analytic formula for a dipole to generate a sequence of (x,y,z) points for a Trail3D Element.
unquote:

may i humbly request for an example for me to work on?
it will greatly enhance my understanding and if i am correct, you will add an new example that does not exist yet on OSP digital library!

thanks Prof Wolfgang.
:)

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Re: Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 06 2012 10:21AM
mrg_psu
5 Posts

I've done some field line tracing in animations, so I've played with this sort of thing before. The impression I get is that tracing field lines is computationally expensive. I threw together a quick and dirty model for a dipole with some commentary (no warranties). Rename the file from .zip to .jar if you want to just run it. I also put it here: http://phys23p.sl.psu.edu/~mrg3/EJS_betas/ejs_fieldlines_3D.jar

I'm not sure if this is exactly what Wolfgang meant.

Let me know if this helps. -Mike Gallis

Attached File: ejs_fieldlines_3D.zip

Re: Re: Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 07 2012 4:12AM

lookang
175 Posts

Thanks mike
it helps!

i also made my own simple model using eclipse equations inspired by General parametric form

http://en.wikipedia.org/wiki/Ellipse
An ellipse in general position can be expressed parametrically as the path of a point (X(t),Y(t)), where

X(t)=X_c + a\,\cos t\,\cos \varphi - b\,\sin t\,\sin\varphi
Y(t)=Y_c + a\,\cos t\,\sin \varphi + b\,\sin t\,\cos\varphi

remove the zip to run as a jar.
:)

Post edited August 7, 2012 at 4:07 AM EST.

Post edited August 7, 2012 at 4:08 AM EST.

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Re: Re: Re: Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 07 2012 4:15AM

lookang
175 Posts

correct file now

Attached File: ejs_fieldlines3D.jar.zip

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Re: Re: Re: Re: Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 07 2012 4:18AM

lookang
175 Posts

added a slider to control the B field strength

Attached File: ejs_fieldlines3D.jar1.zip

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Re: Re: Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 08 2012 2:30PM

lookang
175 Posts

hi prof mike,

i did some editing on your source code and i encountered this runtime error when i try to move the display around.

any idea how to overcome this?

i wonder if this is an error with EJS that requires Paco and Wolfgang's inputs.
thanks!

at org.opensourcephysics.drawing3d.simple3d.SimpleElementTrail.computePositions(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleElementTrail.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Element.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.ElementTrail.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Group.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Group.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.paintDrawableList(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.paintEverything(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.render(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.render(Unknown Source)
at org.opensourcephysics.drawing3d.DrawingPanel3D.render(Unknown Source)
at org.colos.ejs.library.control.drawing3d.ControlDrawingPanel3D.finalUpdate(Unknown Source)
at org.colos.ejs.library.control.EjsControl.finalUpdate(Unknown Source)
at org.colos.ejs.library.Animation.update(Unknown Source)
at org.colos.ejs.library.Animation.step(Unknown Source)
at org.colos.ejs.library.Animation.run(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleElementTrail.computePositions(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleElementTrail.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Element.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.ElementTrail.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Group.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.Group.processChanges(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.paintDrawableList(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.paintEverything(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.render(Unknown Source)
at org.opensourcephysics.drawing3d.simple3d.SimpleDrawingPanel3D.render(Unknown Source)
at org.opensourcephysics.drawing3d.DrawingPanel3D.render(Unknown Source)
at org.colos.ejs.library.control.drawing3d.ControlDrawingPanel3D.finalUpdate(Unknown Source)
at org.colos.ejs.library.control.EjsControl.finalUpdate(Unknown Source)
at org.colos.ejs.library.Animation.update(Unknown Source)
at org.colos.ejs.library.Animation.step(Unknown Source)
at org.colos.ejs.library.Animation.run(Unknown Source)

Attached File: ejs_fieldlines_3Dmike.zip

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Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 11 2012 3:39PM
Wolfgang
103 Posts

I have posted a 3D model showing both field lines and field vectors from a magnetic dipole.

Attached File: DipoleField3D.jpg

Re: Re: possible to draw static magnetic field lines on a bar magnet in 3D - Aug 14 2012 11:31AM

lookang
175 Posts

thanks!
will try to implement them on my remixed models

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