Magnetic field lines

  1. Magnetic field lines do not begin or end; instead, they always form closed paths.

  2. The field lines loop around the currents that cause them.

  3. The field is stronger where the field lines are closer together.

For example, the magnetic field lines generated by a circular loop of wire carrying a current looks like this:

(The lines are shown only in one plane to make it easier to draw -- the full pattern is of course symmetric about the axis of the loop.)

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