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Unformatted text preview: 56. (a) By the righthand rule, B points into the paper at P (see Fig. 306(c)). To ﬁnd the magnitude
of the ﬁeld, we use Eq. 3011 for each semicircle (φ = π rad), and use superposition to obtain the
result:
µ0 iπ µ0 iπ
µ0 i 1 1
B=
+
=
+
.
4πa
4πb
4
ab
(b) The direction of µ is the same as the B found in part (a): into the paper. The enclosed area is
A = (πa2 + πb2 )/2 which means the magnetic dipole moment has magnitude
µ = πi 2
a + b2
2 . ...
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 Fall '08
 SPRUNGER
 Physics

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