Hi prof, this applet is simply fantastic!

the play button seems to work only for the initial conditions.

i moved the slider and click play, it doesn't seems to show the magnetic field lines from the bar magnet.

chance to check it out and enhance it? thanks! :D

i would make x slide able all the way inside the metal coil, it is the calculation is different thus u made it to only move on the one side of the coil?
It would be a great tool if they can explore left, centre and right of the coil.
for ur consideration!