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Unformatted text preview: 45. We use Eq. 2920 B = µ 0ir / 2π a 2 for the Bfield inside the wire ( r < a ) and Eq. 2917
B = µ 0i / 2π r for that outside the wire (r > a).
(a) At r = 0, B = 0 .
(b) At r = 0.0100m , B = µ 0ir (4π×10−7 T ⋅ m/A)(170A)(0.0100m)
=
= 8.50 ×10−4 T.
2
2
2π a
2π (0.0200m) (c) At r = a = 0.0200m , B = (d) At r = 0.0400m , B = µ 0ir (4π×10−7 T ⋅ m/A)(170A)(0.0200m)
=
= 1.70 ×10−3 T.
2π a 2
2π (0.0200m) 2 µ 0i (4π×10−7 T ⋅ m/A)(170A)
=
= 8.50 ×10−4 T.
2π r
2π (0.0400m) ...
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 Spring '08
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 Physics

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