Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Using asingle compass needle, the student should verify the diagrams andmake notebook sketches, ELECTR OMA GNETISM 157 168. Deflection of a Horizontal Magnetic Needle.— When a wire is held horizontally over a poised magneticneedle, pointing N and S (or in the magnetic meridian), , and a current passed through it, the needle is deflectedand tends to take up a position at right angles to the the current is sufficiently strong, the needle moves, sothat it will accommoda
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Using asingle compass needle, the student should verify the diagrams andmake notebook sketches, ELECTR OMA GNETISM 157 168. Deflection of a Horizontal Magnetic Needle.— When a wire is held horizontally over a poised magneticneedle, pointing N and S (or in the magnetic meridian), , and a current passed through it, the needle is deflectedand tends to take up a position at right angles to the the current is sufficiently strong, the needle moves, sothat it will accommodate through itself the greatest numberof magnetic lines of the circular field, and also to such a posi-tion that its own natural magnetic lines will be in the samedirection as the currents lines of force. Considering Fig. 134, the current flows over the needle fromright to left (also N to S). As you look along the wire in thedirection of the current the direction of the whirls is right-handed or clockwise, as indicated by the dotted circles inFig. 134, and also on the lower diagram of Fig. 136, the N-pole. E F G Fig. 135.—Resultant Deflections of the Magnetic Needle When Placed Nearto a Current-Carrying Wire. of the needle, N„ moves to the position, N2, at right angles tothe wire, and in the direction of the field underneath the wire(which is from S2 to N2), so that the direction of the whirlsand the needles natural lines are coincident. Consider the right hand, Fig. 134, as N, and the left hand 158 PRACTICAL ELECTRICITY. as S. The direction of the currents field underneath thewire is then from west to east, and the N-pole of the needleis deflected east. When a current flows from North Over a needleto South the N-end is deflected East. See A of Fig. 135. Thismay be remembered by the combination of the above letters, which forms theo + ? t
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