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.