M =
R
[r
0
j]dV
0
/2c
jdV
0
= j(dl
0
dS
0
) = dIdl
0
S =
R
[r
0
dl
0
]/2
j =
X
i
e
i
v
i
δ(r − r
i
),
m
i
e
i
/m
i
H H = ∇ ×
A
dl
jdV
1
= Idl
dU dl
dU
A =
1
c
Z
j(r
0
)dV
0
R
,
∇ × fA = f ∇ × A + [∇f, A],
r r
0
dl
0
dr
dH =
dI
c
[dl
0
R]
R
3
,
R
R =
√
r
2
+ z
2
r z
dI = 2rdr/(b
2
− a
2
)
