STATIC FIELDS

You have observed the attraction between opposite poles of magnets and the repulsion between like poles. Similar effects occur with electrically charged objects. These forces seem to operate only over short distances under laboratory conditions, but this is so because such fields weaken rapidly, as the distance between poles increases to less than the smallest intensity we can detect. In theory, the fields extend into space indefinitely.

A constant electric current in a wire produces a magnetic field around the wire. The lines of magnetic flux are perpendicular to the direction of the current. The existence of a constant voltage difference between two nearby objects produces an electrical field; the lines of electrical flux are parallel to the gradient of the charge differential. When the intensity of a current or voltage changes with time, things get more interesting.