56 



ELECTRICAL ENGINEERING 



on the coil by the pole is equal and opposite to the force exerted 

 on the pole by the coil. 



/Cos0 



m 



FIG. 46. Intensity of the magnetic field on the axis of a short coil. 



The field intensity at the wire due to the pole m at P is -7 



m 



dynes and the flux density is -^ lines per square centimeter, where 



d cm. is the distance from the point to the wire; the length of 

 wire is 2 wrn cm. and therefore the force exerted on it is 





/ = X 2 irrnl dynes. 



This force acts at right angles to the lines of flux and may be 

 resolved into two components, / cos 6 in the plane of the coil and 

 / sin d perpendicular to the plane of the Coil. The component 

 / cos 6 taken around the loop is zero and therefore the com- 

 ponent / sin is equal in magnitude to the force racJ-C. 



