Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . currentthrough the electromagnet. The magnetic field of the electro-magnet is nearly at right angles to thefield of the wire, and the wire rotatesabout the pole, when the current is passed through it, accord-ing to the principle that a magnetic body free to move, tends tomove so that its lines of force willbe in the same direction as the linesof the field in which it is placed. The direction of rotation canbe determined before the currentis turned on by the following left-hand ride:
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . currentthrough the electromagnet. The magnetic field of the electro-magnet is nearly at right angles to thefield of the wire, and the wire rotatesabout the pole, when the current is passed through it, accord-ing to the principle that a magnetic body free to move, tends tomove so that its lines of force willbe in the same direction as the linesof the field in which it is placed. The direction of rotation canbe determined before the currentis turned on by the following left-hand ride: Place the thumb, first and secondfingers of the left hand all at rightangles to each other, as in Fig. 2J/.3,and the hand so that the first fingerindicates the direction of the linesof force of the magnet, and the secondfinger the direction of the current inthe wire; the thumb will then in-dicate the direction of motion of thewire. Applying the left-hand rule to Fig. 242, we find thatthe wire will rotate in the direction opposite to the handsof the clock. It tends to wind around the pole in such Left Hand. Fig. 243.—Left-Hand Rule for Determining the Direction of Rotation of a Moving AVire in a Magnetic rule applies to motors. ELECTR OD YNAMICS. 279 a direction as to increase the magnetism of the pole, just asin the automatic twisting experiment, *\\ 266. This rule is very convenient for determining the directionof rotation of motors, ^f 358. The moving wire in Fig. 242is analogous to the armature of the motor, and the electro-magnet, its field. If the direction of current through the armature and field ofFig. 242 be reversed, as by changing the binding post ter-minals, the direction of rotation will be the same as be-fore, because the current through the moving wire and thepolarity of the field are both reversed, therefore, the same re-lation exists as before, which can be proved by the left-handrule. If, now, only the current in the wire be reversed, oronly the p
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