DC MOTOR THEORYDC MotorsTheoryofOperationFigure 1 Left-Hand Rule forCurrent-Carrying ConductorsEvery current-carrying conductor has a magneticfield around it. The direction of this magneticfield may be found by using the left-hand rule forcurrent-carrying conductors. When the thumbpoints in the direction of current flow, the fingerswill point in the direction of the magnetic fieldproduced, as shown in Figure 1.If a current-carrying conductor is placed in amagnetic field, the combined fields will besimilar to those shown in Figure 2. The directionof current flow through the conductor is indicatedwith an "x" or a "·". The "x" indicates thecurrent flow is away from the reader, or into thepage. The "·" indicates the current flow istowards the reader, or out of the page.Above the conductor on the left, the field caused by the conductor is in the opposite directionFigure 2 Current-Carrying Conductor in a Magnetic Fieldof the main field, and therefore, opposes the main field. Below the conductor on the left, thefield caused by the conductor is in the same direction as the main field, and therefore, aids themain field. The net result is that above the conductor the main field is weakened, or flux densityis decreased; below the conductor the field is strengthened, or flux density is increased. A forceis developed on the conductor that moves the conductor in the direction of the weakened field(upward).ES-06 Page 2 Rev. 0
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