19(a)]
1
B
∝r
(r > a)
Now the current enclosed Ie is not I, but is less than this value Since the current distribution is uniform, the current enclosed is,
I
I
ar
e =




π
π
2
2
 
2
2
aIr
=
Using Ampere’s law, 
π
2
0
2
(2
)
I r
B
r
a
µ
=
B
aI
r
= 


µ0
2
2�
[4 19(b)]
B µ r      (r < a)
FIGURE 4 14
Figure (4