Chap. 10] 



ELECTRICAL METHODS 



801 



(Fig. 10-117). It should be noted that these experiments represent a 

 combination of electromagnetic and inductive methods, excitation being 

 produced by a long grounded cable. Hence, the effects of current con- 

 centration due to conduction are superimposed upon those due to induction. 



I so 



% 70 

 i^ 60 



% ^ 

 "I- ^^ 



%90 

 %20 



1 



loop Plane 



3.2cm 



40 50 



Coordinates 



60 70 80 90 too 



(a) 



_L 



Loop Plane 



Verlkol Component Z 

 Horizontal Component V 



40 50 



Coordinates 



60 



70 



100 



(b) 



Fig. 10-116. Vertical and horizontal components (without regard to phase) of 

 induced electromagnetic field for: (a) vertical ore body, and (b) dipping ore body, 

 in center of rectangular loop (after Sundberg). 



The former produce largely the in-phase (P) component, while the latter 

 give rise to the quadrature (Q) component. The current concentrations 

 for the Q component are near the edge of the conductor (skin effect), while 

 those responsible for the P component are more toward the interior of 

 the conductor. 



