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Unformatted text preview: 56. (a) By the right-hand rule, B points into the paper at P (see Fig. 30-6(c)). To ﬁnd the magnitude
of the ﬁeld, we use Eq. 30-11 for each semicircle (φ = π rad), and use superposition to obtain the
µ0 iπ µ0 iπ
µ0 i 1 1
(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