102 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



A 



magnetized strip 

 of steel 



S 

 side view 



end pjr 



Fig. 66. 



a portion of the polar edge NNNN and a portion of the wire AB each / centi- 

 meters in length. The intensity H f of the magnetic field at the wire due to the pole 

 NNNN is equal to 2m/rt, according to equation (20), and. the wire AB is pushed 

 sidewise by a force F f which is equal to /X^X 2w /^i according to equation 

 (28), but the force with which the pole NNNN acts on the wire is equal and oppo- 

 site to the force mH (see Fig. 66) with which the wire acts on the pole. Therefore, 

 ignoring signs, we have ;//=//X zmjrl, whence 



H ~7 (33) 



\ 



56. Magnetic field inside of a long solenoid. A solenoid is a 

 winding of wire on a long tube as shown in Fig. 67, which is a 

 sectional view. When an electric current flows through the wind- 

 ing of a solenoid the region inside of the solenoid becomes a 

 uniform magnetic field except near the ends of the solenoid as 



G Q 000 e OS Q0!3e> 



Fig. 67. 



