This preview shows page 1. Sign up to view the full content.
Unformatted text preview: 78. By the righthand 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
xcomponents survive, yielding
B1 + B2 = 2 µ0 i
cos 150◦ ˆ = −3.46 × 10−5 ˆ T
i
i
2π where i = 10 A, = 0.10 m, and Eq. 306 has been used. To cancel this, wire b must carry current into
ˆ
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. 306 has again been used. ...
View
Full
Document
 Fall '08
 SPRUNGER
 Physics

Click to edit the document details