Electricity and Magnetism

Chapter 39

Mutual Inductance

Thus far, we’ve considered how one circuit loop, or a single multi-loop coil,

1

reacts induc-

tively to the current flowing through it. Now, let’s consider two such coils in proximity. To

facilitate our analysis we shall assume that Coil

1

has N

1

turns and bears current I

1

, while

Coil

2

has N

2

turns and carries I

2

. Furthermore, these coils are assumed to share a common

axis, as illustrated in Figure 39.1.

Common axis of

symmetry

Current flowing

into the page

Current flowing

out of the page

Loop 1 Loop 2

⊙I

1

⊗I

1

⊙I

2

⊗I

2

FIGURE 39.1 Two Current-Carrying Coils Sharing a Common Axis

The current flowing in Coil

1

produces a magnetic field throughout