74. We use the expression for the flux Φ
B
over the toroid cross-section derived in our solution to problem 52
obtain the coil-toroid mutual inductance:
M
ct
=
N
c
Φ
ct
i
t
=
N
c
i
t
µ
0
i
t
N
t
h
2π
ln
b
a
=
µ
0
N
1
N
2
h
2π
ln
b
a
where N
t
= N
1
and N
c
= N
2
. We note that the formula for Φ
B
can also be found in the Supplement
for the chapter, in Sample Problem 31-11.