Field of Force of a Current.
A current establishes a field of force around itself, whose lines of
force form circles with their centres on the axis of the current. The
cut, Fig. 172, shows the relation of lines of force to current.
Fig. 171. EXPERIMENT SHOWING LINES OF FORCE
SURROUNDING AN ACTIVE CONDUCTOR.
Fig. 172. DIAGRAM OF FIELD OF FORCE SURROUNDING AN ACTIVE CONDUCTOR.
Fig. 173. LINK OF FORCE INDUCED BY A CURRENT SHOWING THE MAGNETIC WHIRLS.
The existence of the field is easily shown by passing a conductor
vertically through a horizontal card. On causing a current to go through
the wire the field is formed, and iron filings dropped upon the card,
tend, when the latter is gently tapped, to take the form of circles. The
experiment gives a version of the well-known magnetic figures, q. v. See
Fig. 171.
The cut shows by the arrows the relation of directions of current to the
direction of the lines of force, both being assumptions, and merely
indicating certain fixed relations, corresponding exactly to the
relations expressed by the directions of electro-magnetic or magnetic
lines of force