9
=




21
0
2
0
2
(
)
µ
µ
n Al
B
n
        [from Eq (6 15)]
2
0
21
µB Al
=
(b)
The magnetic energy per unit volume is,
B
B
U
u
=V
            (where V is volume that contains flux)
      
UB
Al
=
      
2
20
B
µ
=
(6 18)
We have already obtained the relation for the electrostatic energy
stored per unit volume in a parallel plate capacitor (refer to Chapter 2,
Eq