P27_004.PDF

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Chapter 27 - 27.4
4. (a) The magnitude of the current density vector is
J =
i
A =
i
πd 2 / 4
=
4(1 . 2
×
10 10 A)
=2 . 4
×
10 5 A / m 2
.
π (2 . 5
×
10 3 m) 2
(b) The drift speed of the current-carrying electrons is
v d =
J
ne =
2 . 4
×
10 5 A / m 2
=1 . 8
×
10 15 m / s .
(8 . 47
×
10 28 / m 3 )(1 . 60
×
10 19 C)
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