356 ELEMENTS OF ELECTRICAL ENGINEERING. 



strength of the current in the wire in abamperes. When the 

 current is expressed in amperes we have : 



ff^^-Zl (3*) 



10 



6, Units of magnetomotive force. The product, tC, of the length 

 of path in centimeters and intensity of magnetic field in gausses, 

 gives the magnetomotive force along the path (when / and &C are 

 parallel, of course) in c.g.s. units. The name gilbert has been 

 adopted by the American Institute of Electrical Engineers for 

 the c.g.s. unit of magnetomotive force. 



7 he ampere-turn. The magnetomotive force along a path 

 which links with one turn of wire carrying one ampere of current 

 is called one ampere-turn. The magnetomotive force of any coil, 

 in ampere-turns, is equal to the product of the current flowing in 

 the coil in amperes multiplied by the number of turns of wire in 

 the coil. In magnetic calculations it is usually convenient to 

 reduce ampere-turns of magnetomotive force to c.g.s. units (gil- 

 berts), which is done by multiplying ampere-turns by 47r/io, 

 according to equation (3^). 



The product of field intensity into length of path gives mag- 

 netomotive force, so that the quotient obtained by dividing mag- 

 netomotive force by length of path is field intensity. When a 

 magnetomotive force expressed in ampere turns is divided by 

 length of path we have a magnetic field intensity expressed in 

 ampere-turns-per-centimeter, or in ampere-turns-per-inch y as the 

 case may be. 



7. Magnetizing force in iron. When an iron rod is placed in 

 a magnetic field and is magnetized thereby, the actual magnetic 

 field along the rod depends upon the cause of the original field 

 and also upon the newly created magnetic poles of the rod itself. 

 Thus when an iron rod is placed in a coil of wire through which 

 an electric current is flowing, the field along the rod is due to the 

 combined action of the coil and the poles of the re d. 



