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20.74. Set Up:
Ampere’s law says that the sum of
around any closed curve equals
where
is the
net current encircled by the curve.
Solve:
so
20.75. Set Up:
The field lines are circles centered on the conductor. By symmetry, the magnitude of the field
depends only on the distance from the wire. Ampere’s law says
Apply this law to a circular path
with radius
r
and with the wire at its center.
Solve:
On the path
is tangent to the path and constant, so
the current in
the wire. Ampere’s law therefore gives
and
20.76. Set Up:
Apply Ampere’s law to a circle of radius
r
that has the axis of the conductors at its center. By
symmetry
is constant on this circle and is tangent to it, so
Solve: (a)
For
the current in the inner conductor. Ampere’s law says
(b)
For
Since the circle encloses both conductors and they carry currents in opposite directions.
Ampere’s law says
and
20.77. Set Up:
A sketch of a cross section in a plane perpendicular to the common axis of the conductors is given
in Figure 20.77. Let the inner conductor have current
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This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.
 Spring '07
 Shoberg
 Current, Force

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