ADVANCED ELECTRICITY AND MAGNETISM 



magnet poles, a north pole and a south pole, facing each other. 

 The filaments of iron filings show what are called the lines of 

 force of the magnetic field; a line of force being a line drawn so as 

 to be at each point in the direction of the field at that point. The 

 magnetic field in the central region in Fig. 50 is approximately 

 uniform. 



Figure 56 represents a small magnet held in the approximately 

 uniform magnetic field between two large magnet poles, and the 

 arrows represent the equal and opposite forces which are exerted 

 on the small magnet by the approximately uniform field. 



N 



Fig. 5b. 

 The arrows show the forces which act upon the poles of the small magnet. 



The force H (in dynes) which a magnetic field exerts upon a 

 unit test pole is used as a measure of the intensity or strength 

 of the magnetic field, and this force-per-unit-pole is hereafter 

 spoken of simply as the intensity or strength of the field. The 

 unit of magnetic field intensity (one dyne per unit pole) is called 

 a gauss. That is, a magnetic field has an intensity of one gauss 

 when it will exert a force of one dyne upon a unit pole. 



Complete expression for the force exerted on a magnet pole 

 by a magnetic field. A magnetic field of which the intensity is 

 H gausses exerts a force of H dynes upon a unit pole as above 

 explained, and it exerts a force of mil dynes upon a pole of 

 which the strength is m units. That is: 



F = mH (i) 



in which F is the force in dynes which is exerted on a pole of 

 strength m by a field of intensity H. 



