ELEMENTARY LAWS OF CONTINUOUS CURRENTS 23 



of the lines of force of the field and the middle finger (held 

 at right angles with the index finger) points in the opposite 

 direction to the current, then the conductor will tend to 

 move in the direction of the outstretched thumb. 



If the direction of either is reversed the direction of the 

 force acting on the conductor is reversed; if the direction 

 of the current in the conductor and the direction of the 

 magnetic field are both reversed, the direction of the force 

 acting on the conductor remains unaltered. 



Magnitude of the Force. The magnitude of the force 

 depends upon the length of conductor perpendicular to 

 the direction of the field, the amount of current sent through 

 the conductor, and the density of the magnetic field in 

 which the conductor is placed. 



If Z = the length in cms. of the conductor perpendicular 



to the direction of the magnetic field; 

 // = the strength of the magnetic field in gausses; 

 7 = the current through the conductor, in amperes; 



Then, 



Force (in dynes) =IHI/ 10 (13) 



If the total length of the conductor is I' and the angle 

 between the direction of the conductor and the magnetic 

 field is 0, 1 = 1' sin 0; so that we may write 



Force (in dynes) = I' HI sin 0/10. . . (14) 



If the force is desired in terms of English units we have 



Force (in pounds) = .886/7/7 sin 0X10' 7 , . (15) 



where I' is expressed in inches, H in lines per sq.in. and I 

 in amperes. 



