Hence, 
....................................(7.14)
In the static case, 
and 
and Eq(7.14) simplifies to
...............................................................(7.15)
For , eqn(7.10) simplifies to
.......................................................(7.16)
(7.16) is recognized to be as the Poisson's equation and therefore the solution can be written as,
..................................................(7.17)
and 
where C1 and C2 are constants. Out of these two solutions,