Magnet Moving In And Out Of A Coil

A video of the classic experiment showing a current in a coil when a magnet is moved into and out of a coil.

An animation of the magnetic field lines in the experiment above when the magnet is pulled out of the coil. The details of how the current in the coil and thus the total magnetic field (magnet plus coil) is calculated are given in the pdf document referenced above. Qualitatively, the field lines have a hard time moving across the conducting ring (they get "hung up") which is a qualitative explanation of why the experimenter must expend energy to move the magnet out of the coil. This is an example of the tension exerted parallel to the field--the field line tension both pulls on the coil and on the hand of the experimenter, trying to keep them from moving apart.

An animation of the magnetic field lines in the experiment above when the magnet is pulled out of the coil. This time we show only one field line at a given latitude, but repeat that field line every 15 degrees about the symmetry axis of the coil and magnet. We have also reduced the resistance of the coil by a factor of three, so that the effect of the eddy currents in the coil are more pronounced.

An animation of the magnetic field lines when the magnet is pushed toward the coil (with the resistance of the coil back up to the value in our original animation). Again the field lines get hung up when the experimenter tries to push them across the coil. This is an example of the pressure exerted perpendicular to the field--the field pressure in this configuration pushes both on the coil and the hand of the experimenter, trying to keep them from coming together.