Homework Help: Current density and vector potential

1. Sep 20, 2010

oddiseas

1. The problem statement, all variables and given/known data

What current density would produce the vector potential
A(r)=(-kmu/2pi)In(r/a) (in the z direction)

where k is a constant, in cylindrical coordinates?

2. Relevant equations

3. The attempt at a solution

i have done this three times and i get zero current density.So i am wondering if i am making a mistake, there is only one component for A the z component so when i use B=grad*A, i get a field in the fita direction, then when i use J=(grad*B)/mu i get zero.

2. Sep 20, 2010

gabbagabbahey

Hint: $\frac{r}{r}$ is undefined at $r=0$