Magnetic Fields - Continued

Electronic Principles
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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.