# amperes law question..

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#### transgalactic

##### Banned
here is a question:
http://i25.tinypic.com/fc8rqr.jpg

there is endless cylinder i which we only see its crossection in the photo.
its radius is $R_1$ a distance d from the center a cylinder with radius $R_2$
along the cylinder flows current I in a uniform way inside the page(X).
1.what is the magnetic field in x>0 region?
2.what is the magnetic field in (0,$R_1$)?

i tried to solve it by amperes law
$\oint \vec{B}\vec{dl}=\mu_0 I$
0<r<d
$\oint \vec{B}\vec{dl}=\mu_0 I\\$
$I_0=I\frac{\pi r^2}{\pi R_1^2}=I\frac{ r^2}{R_1^2}\\$
$B =\mu_0 I\frac{ r^2}{R_1^2 2\pi r}\\$

have i done the first region correctly

#### transgalactic

##### Banned
dl vector is the way we are going
but we can go clock wise and counter clock wise
and in each case i will have a different result
??

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