Did you know that energy can be store in and release from a rubber band? I guess that we have all tried to put energy into a rubber band by stretching or twisting it. When the rubber band is released again, it releases the energy that was stored in it. Surprised? Do you remember the feeling when one end of a stretched rubber band suddenly slips your fingers? I do, the slap it gives the other hand can be a little painful. This slap is where the energy that was put into stretching rubber band it is converted into heat.
You may also use a rubber band as a simple motor for a small model airplane. If one end of the rubber band is attached to a propeller and the other end to the body of the airplane. Then, by winding up the rubber band the twist stores energy that can be used to get the propeller to rotate and drag the plane through the air.
The magnetic field is capable of something similar. Energy can be stored in the magnetic field by stretching, bending and twisting it. But is in not generally possible to let go of one end of the magnetic field and release the stored energy. Instead it is possible to "cut" two magnetic field lines and reconnect them in a different way. It sounds like magic!
You can get some idea of what happens by putting your thumb and forefinger on both hands together to make two linked "rings". Now try to get the two rings apart without breaking the contact between your thumb and forefinger on the two hands - impossible, unless you are cheating! If you instead allow the two thumbs and the two forefingers to connect when the two "rings" get close together, then you can change the two rings into one bigger ring. This is in principle what the magnetic field can do and thereby release some of the energy it contains!
Below is a simple animation that shows how field lines are transported into the region where the magnetic field lines can be reconnected. The colours indicate which regions they initially come from. The "cut and glue" effect takes place in the shaded region in the center.
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