DC Motors DC MOTOR THEORYAbove the conductor on the right, the field caused by the conductor is in the same direction asthe main field, and therefore, aids the main field. Below the conductor on the right, the fieldcaused by the conductor is in the opposite direction of the main field, and therefore, opposes themain field. The net result is that above the conductor the field is strengthened, or flux densityis increased, and below the conductor, the field is weakened, or flux density is decreased. Aforce is developed on the conductor that moves the conductor in the direction of the weakenedfield (downward).In a DC motor, the conductor will be formedFigure 3 Motor Actionin a loop such that two parts of the conductorare in the magnetic field at the same time, asshown in Figure 3.This combines the effects of both conductorsto distort the main magnetic field and producea force on each part of the conductor. Whenthe conductor is placed on a rotor, the forceexerted on the conductors will cause the rotorto rotate clockwise, as shown on Figure 3.You can think of these magnetic lines of forceas rubber bands that are always trying toshorten themselves. The lines of force abovethe conductor exert a downward force due tothe magnetic lines of force trying to straighten themselves.The above explanation of how aFigure 4 Right-Hand Rule for Motorsforce is developed is convenient;however, it is somewhat artificial.It is based on a fundamentalprinciple of physics which may bestated as follows:"A current-carrying conductor in amagnetic field tends to move atright angles to that field."Another important way to showthe relationship between thecurrent-carrying conductor,magnetic field, and motion, is theright-hand rule for motors, asshown in Figure 4.Rev. 0 Page 3 ES-06
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