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Unformatted text preview: 78. By the right-hand rule, the magnetic ﬁeld B1 (evaluated at a) produced by wire 1 (the wire at bottom
left) is at φ = 150◦ (measured counterclockwise from the +x axis, in the xy plane), and the ﬁeld produced
by wire 2 (the wire at bottom right) is at φ = 210◦ . By symmetry (B1 = B2 ) we observe that only the
x-components survive, yielding
B1 + B2 = 2 µ0 i
cos 150◦ ˆ = −3.46 × 10−5 ˆ T
2π where i = 10 A, = 0.10 m, and Eq. 30-6 has been used. To cancel this, wire b must carry current into
the page (that is, the −k direction) of value
ib = 3.46 × 10−5
where r = √ 2π r
= 15 A
µ0 3 /2 = 0.087 m and and Eq. 30-6 has again been used. ...
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- Fall '08