Magnetic Bar Field Model

The EJS Magnetic Bar Field Model shows the field of a bar magnet. It has a movable compass that reports the field magnitude and a grid of magnets that shows the field direction.  The intensity check box will vary the color of the magnet grid to indicate weak and strong field locations.

Exercises:

1. Run the simulation. Move the compass around in the magnetic field of the magnet. Move the magnet around. What is the relation between the compass and the field vector (small arrows)?  
2. Test to see how well you can use the compass to determine the location of the magnet:  Press the Hide Field button and then press the "Set magnet to a random location" button. Use the compass to show the direction of the magnetic field and then move the marker (same size as the magnet) to where you think the magnet is located. Click on Show Field to see if you were correct.  If you were, describe your strategy. If you weren't, explain what went wrong and try again.
3. The bar magnet's field is modeled using magnetic dipoles underneath the bar magnet image.  If you have Ejs installed, examine the model and determine how many dipoles are stacked together (and in what configuration) to model the magnet.  Why is it reasonable to model a magnet using multiple dipoles?  How may dipoles are there in an actual bar magnet?
   

Credits:

The Magnetic Bar Field Model was created by Wolfgang Christian and Francisco Esquembre and modified by Anne J Cox using the Easy Java Simulations (EJS) authoring and modeling tool. Exercises written by Anne J Cox. 

You can examine and modify a compiled EJS model if you run the program by double clicking on the model's jar file.  Right-click within the running program and select "Open EJS Model" from the pop-up menu to copy the model's XML description into EJS.  You must, of course, have EJS installed on your computer.

Information about EJS is available at: <http://www.um.es/fem/Ejs/> and in the OSP ComPADRE collection <http://www.compadre.org/OSP/>.