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ELECTRICAL MACHINERY 



away from the observer and those marked ( ) are carrying 

 current toward the observer. The conductors under pole A 

 carry current away from observer and the flux is directed 

 downward, therefore they will all exert a force toward the 

 left as indicated by the arrow under them. Those under 

 pole C carry current in the same direction as those under 

 A but the direction of the field is upward therefore the 

 force is toward the right as shown' by the arrow under pole 

 C. The conductors under the two poles B and D give 



Field of strength ='H 



FIG. 95. A Conductor of Length I, Perpendicular to the Magnetic 

 Field and Carrying a Current /. 



forces up and down respectively as shown by arrows and 

 it is now seen that all conductors tend to turn the arma- 

 ture in the same direction, i.e., counter-clockwise. 



Torque Calculation. To calculate the magnitude of 

 this turning effort we must know the number of conductors 

 lying in the magnetic field, the active length of each con- 

 ductor (i.e., length of conductor under the pole face), 

 strength of field in the air gap where the conductors are 

 situated, and the current carried by the conductors. By 

 the use of formula (1) we can calculate the force in dynes 



