94
0
2
wire
wire
ˆ
4
I
d
d
r
µ
π
×
=
=
∫
∫
s
r
B
B
G
G
G
(9.1.4)
The integral is a vector integral, which means that the expression for
B
G
is really three
integrals, one for each component of
B
G
. The vector nature of this integral appears in the
cross product
ˆ
I d
×
s
r
G
. Understanding how to evaluate this cross product and then
perform the integral will be the key to learning how to use the BiotSavart law.
Interactive Simulation 9.1
: Magnetic Field of a Current Element
Figure 9.1.2 is an interactive ShockWave display that shows the magnetic field of a
current element from Eq. (9.1.1). This interactive display allows you to move the position
of the observer about the source current element to see how moving that position changes
the value of the magnetic field at the position of the observer.
Figure 9.1.2
Magnetic field of a current element.
Example 9.1:
Magnetic Field due to a Finite Straight Wire
A thin, straight wire carrying a current
I
is placed along the
x
axis, as shown in Figure
9.1.3. Evaluate the magnetic field at point
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 Fall '08
 RABE
 Physics, Vector Space, Magnetic Field, 2 L

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