P31_005.PDF

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Chapter 31 - 31.5
5. (a) Table 27-1 gives the resistivity of copper. Thus,
R = ρ L
A =(1 . 68
×
10 8
·
m) π (0 . 10m)
π (2 . 5
×
10 3 ) 2 / 4
=1 . 1
×
10 3 .
(b) We use i =
|E|
/R =
|
d Φ B /dt
|
/R =( πr 2 /R )
|
dB/dt
|
. Thus
dB
dt
= iR
πr 2 = (10A)(1 . 1
10 3 Ω)
π (0 . 05m) 2
×
=1 . 4T / s .
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