Magnetic field due to a long, straight wire

[Meow12]

Homework Statement

A magnetic field of 91.4 T has been achieved at the High Magnetic Field Laboratory in Dresden, Germany. Find the current needed to achieve such a field 2.00 cm from a long, straight wire.

Relevant Equations

Ampere's law: $\displaystyle\oint\vec B\cdot d\vec l=\mu_0 I$

From Ampere's law, $\displaystyle\oint\vec B\cdot d\vec l=\mu_0 I$ where $r$ is the distance from the wire

$B\cdot 2\pi r=\mu_0 I$

$\displaystyle 91.4\times 2\pi\left(\frac{2}{100}\right)=4\pi\times 10^{-7} I$

$I=91.4\times 10^5\ A=9.14\ \rm{MA}$

But the answer given in the textbook is $3.72\ \rm{MA}$. Where have I gone wrong?

 

[TSny]

Your work and your numerical answer look good to me.

 

[Meow12]

Thanks; I guess the textbook is wrong, then.

 

[Delta2]

I also agree, but try to find the distance such that the total current is as textbook says.

I mean to find the distance from the wire such that at this distance the magnetic field is 91.4T when the wire carries 3.72MA