INTERACTIONS OF MOVING ELECTRONS 201 



electrons flying apart, but they would have no tendency 

 to do so. 



If two equal circular loops are placed with their 

 planes parallel as in Fig. 21, so that the distance between 

 them is everywhere the same, then it is found that the 

 force of attraction is proportional to the two currents 

 and inversely as the distance between 

 them and also directly proportional 

 to the length of the current path. // / i u 

 If one of the loops is formed of U I / // 

 several turns of wire, since the same 

 current will travel through each turn, 

 the effect will be increased propor- 

 tionately to the number of turns. 

 If the current hi one of the loops is 

 reversed, then there is a repulsion 

 equal to the former attraction. For convenience hi 

 determining for any pair of such circuits whether the 

 action is one of repulsion or of attraction it is simplest 

 to view both circuits from some point which is not 

 between their planes. If the currents are in the same 

 direction there is attraction, and if hi opposite direc- 

 tions there is repulsion Incidentally, it is obvious 

 that in a coil of several turns the various turns are 

 mutually attracted. 



Consider the case of a fixed coil, ab, and a movable 

 coil, cd, shown in Fig. 22, both carrying currents in 

 the direction of the arrows. The interactions of the 

 electrons hi wires a and c cause them to pellate while 

 wires a and d tractate. The result is that the coil cd 

 rotates in the direction of the heavy arrow. A rule 

 may now be stated for the rotation of a movable coil 



