14 ADVANCED ELECTRICITY AND MAGNETISM. 



where m is the strength of each of the poles of the big magnet. 

 Furthermore, we have from Fig. 14: 



A 

 IT 



Therefore, using the above expression for h we get equation (2). 



tan = , 



PROBLEMS. 



I. Two permanent magnets I centimeter X 0.5 centimeter 

 X 30 centimeters long are magnetized to an intensity of 700 units 

 pole per square centimeter of sectional area, (a) Calculate the 

 strength of each pole, (b) Calculate the force with which the 

 north pole of one rod attracts the south pole of the other rod 

 when the poles are at an approximate distance of 10 centimeters 

 from each other. Ans. (a) 350 units pole, (b) 1,225 dynes. 



Note. In this and the following problems, assume the poles of the magnet to 

 be concentrated at the center of the ends of the bars. The intensity of magnetiza- 

 tion of an iron rod is the strength of pole on one end divided by the sectional area 

 of the rod. 



S _ N S _ If 



'< . ' ' i 



Fig. p2. 



2. The two magnets specified in problem I are arranged as 

 shown in Fig. p2. Find the total force with which one magnet 

 acts upon the other magnet. Ans. 227.39 dynes attraction. 



\20 cm. 



< JBTcSZ, 



Fig. p3. 



3. The two magnets specified in problem I are arranged as 

 shown in Fig. 3. Find the total force with which one magnet 

 acts on the other magnet. Ans. 507.8 dynes repulsion. 



