26. We use J = σE = (n
+
+ n
−
)ev
d
, which combines Eq. 27-13 and Eq. 27-7.
(a) The driftvelocity is
v
d
=
σE
(n
+
+ n
−
)e
=
(2.70
× 10
−14
/Ω
·m)(120 V/m)
[(620 + 550)/cm
3
](1.60
× 10
−19
C)
= 1.73 cm/s .
(b) J = σE = (2.70
× 10
−14
/ Ω
·m)(120 V/m) = 3.24 × 10
−12
A/m
2
.