g/Discussion question A.
h/Discussion question B.
i/Discussion question C.
j/Discussion question D.
k/Discussion question E.
have information about a field. On the right is information about
the field’s sources.
It is vitally important to realize that these equations are only
true for statics. They are incorrect if the distribution of charges
or currents is changing over time. For example, we saw on page
620 that the changing magnetic field in an inductor gives rise to
an electric field. Such an effect is completely inconsistent with the
static version of Maxwell’s equations; the equations don’t even refer
to time, so if the magnetic field is changing over time, they will
not do anything special. The extension of Maxwell’s equations to
nonstatic fields is discussed in section 11.6.
Discussion Questions
A Figure g/1 shows a wire with a circular Amperian surface drawn`
around its waist; in this situation, Ampere’s law can be verified easily`
based on the equation for the field of a wire. In panel 2, a second wire has
been added. Explain why it’s plausible that Ampere’s law still holds.`
B Figure h is like figure g, but now the second wire is perpendicular
to the first, and lies in the plane of, and outside of, the Amperian surface.`
Carry out a similar analysis.
C This discussion question is similar to questions A and B, but now the
Amperian surface has been moved off center.`
D The left-hand wire has been nudged over a little. Analyze as before.
E You know what to do.704 Chapter 11 Electromagnetism