# EMM question

1. Sep 8, 2009

### fredrick08

urgent EMM question

1. The problem statement, all variables and given/known data
find the vector potential a distance s from an infinite straight wire carrying current I, check that dell dot A=0 and dellxA=B...

ok i know the answer is A=A(s) z, in cylindricals. A(s)=(mu*I/2*pi)ln(s/a)z when a is a constant.

can someone please explain to me why A points in the same direction as I????

please, i need this asap, because i have no idea.

Last edited: Sep 8, 2009
2. Sep 9, 2009

### kuruman

Re: urgent EMM question

$$\vec{A}=\frac{\mu_{0}}{4\pi}\int_{V}\frac{\vec{J}}{|\vec{r}-\vec{r}\:'|}d^{3}r'$$

For an infinite straight wire, the direction of the current density J is fixed. Therefore ...

3. Sep 9, 2009

### fredrick08

Re: urgent EMM question

Thankyou! = )