U2 
Dr. T. H. Havelock on 
§ 4. Short Coil inside a Long Coil. 
Another case is that of a coil of length 2/^ within 
concentric coaxial coil of length 2 k 2 , as in the figure. 
Fi*. 4. 
■2'a, 
"Zl 
----- > 
Then if % and n 2 are the turns per unit length, we have 
e -h | x-x I ( / tl / 
c J— ^1 J ~»2 
= 8^ate 1 n 2 g/« 1 -^J(^^ 1 -^ / ^) J 1 WJ 1 (^)J], • (27) 
Hence, i£ li 2 — li\ is large compared with 6, a suitable series 
can be obtained by using (12) in these two integrals. We 
find 
The general term can be obtained from (12) if required : 
