

THE MAGNETIC MEASUREMENT OF CURRENT. 29 



turns of wire in the coil, / is the current in the coil in abamperes, 

 and H is the intensity of the field in gausses. Multiplying 



two fine suspending wires 



top view 



side view 



Fig. 24. 



The two sides of the coil in the side view are pushed towards and away from 

 the reader respectively as indicated hi the top view. 



each force F by its lever arm and adding the two results, 



we get the torque T which tends to turn the coil around the 

 axis of suspension. That is: 



T = blZIH (i) 



Case II. Circular coil with its plane parallel to the field as 

 shown in Fig. 25. The vertical dotted line in Figs. 25 and 26 

 is the axis about which the torque is to be determined. Consider 

 an element A/ of the coil. The length of wire in this element is 

 Z-A/ where Z is the number of turns of wire in the coil. The 

 resolved part of H at right angles to A/ is H sin 9, and the 

 side force F (perpendicular to the plane of the paper in Fig. 26) 

 exerted on A/ is Z-A/ X I X ff sin 0. The perpendicular 

 distance of A/ from the axis in Fig. 26 is r sin 6, so that the 

 torque action of F is A T = Fr sin 0. That is : 



AT = rZ/#sin 2 0-A/ (2) 



