, , .
.
, I r (.4.4).
(), x, , ( x = ∞): U = φ φ∞, . U = φ.
E = j ρ,
j = I / S S = 2πx2, x , ρ .
ρ , , . ρ , .
dxdUX = EXdx = j ρdx = { Iρ/ (2πx2)} dx.
x , ( ) :
. 4.4.
, , , . , 20 .
, , . φ U U = φ = Iρ/ (2πr).
U I, : R = U /I = ρ/2πr. (ρ) (r).
I , , , . , U = IR.
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, . (U) x 1 x 2 (), : U = φ1 - φ2 = Iρ (1/ x 1 1/ x 2) / (2π), x 1 ≤ x 2.
L = x 2 x 1. , . , , .