ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
this electromagnetic force produced by the current by placing a
compass at various points on the cardboard and noting the
compass needle deflection. The direction of the magnetic force
is assumed to be the direction in which the north pole of the
compass points.
In figure 53, view A, on the previous page, the needle
deflections show that a magnetic field exists in the circular
form around the conductor. When the current flows upward
(figure 53, view A), the direction of the field is clockwise, as
viewed from the top. However, if you reverse the polarity of
the battery so that the current flows downward (figure 53, view
B), the direction of the field is counterclockwise.
The relation between the direction of the magnetic lines of
force around a conductor and the direction of current in the
conductor may be determined by means of the LEFTHAND RULE FOR A
CONDUCTOR: if you grasp the conductor in your left hand with
the thumb extended in the direction of the electron flow
(current ( to +), your fingers point in the direction of the
magnetic lines of force. Now apply this rule to figure 54 (on
the following page). Note that your fingers point in the
direction of the north pole of the compass points when it is
placed in the magnetic field surrounding the wire.
An arrow is generally used( in electrical diagrams to denote the
direction of current in a length of wire (figure 54, view A).
Where across section of a wire is shown, an end view of the
arrow is used. A crosssectional view of a conductor that is
carrying current toward the observer is illustrated in figure
5,1, view B. Note that the direction of current is indicated by
a (dot, representing the head of the arrow. A conductor that is
carrying current away from the observer is illustrated in figure
54, view C. Note that the direction of current is indicated by
a cross, representing the tail of the arrow. Also note that the
magnetic field around a currentcarrying conductor is
perpendicular to the conductor, and that the magnetic lines of
force are equal along all parts of the conductor.
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