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EAD 234A: E&M
Homework #5
Due Thursday, February 18, 2010
1.
A filamentary current loop traverses eight edges of a cube with side length 2b as shown
below.
(a) Find the magnetic dipole moment m of this structure.
(b) Do you expect a negligible or a nonnegligible magnetic quadrupole moment? Place
the origin of coordinates at the center of the cube as shown.
2.
A current I starts at z =
−∞
and flows up the zaxis as a linear filament until its hits an
origincentered sphere of radius R. The current spreads out uniformly over the surface of
the sphere and flows up lines of longitude from the South Pole to the North Pole. The
recombined current flows thereafter as a linear filament up the zaxis to z = +
∞
.
(a) Find the current density on the sphere.
(b) Use explicitly stated symmetry arguments and Ampere's law in integral form to find the
magnetic field at every point in space.
(c) Check that your solution satisfies the magnetic field matching conditions at the surface of the
sphere.
3.
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 Spring '10
 NCL

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