# In what position can a current-carrying loop of wire be located in a magnetic field so that it doesn't tend to rotate?

I understand that if the wire is not aligned with the magnetic field, it won't rotate, but I'm still confused on how so. Also, which direction is the current flowing?

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Hi Ken to Physics.SE, all you need to know to answer your question is what the Lorentz force is. If a charged particle moves in a magnetic field the Lorentz force will influence it, have a look at en.wikipedia.org/wiki/Lorentz_force. – Alexander Feb 28 '12 at 20:31

## 1 Answer

The current loop will have a magnetic moment $\vec{\mu}$, the direction of which you can get using the right hand rule. It will be orthogonal to the plane of the loop. The torque on the loop will be proportional to $\vec{B}\times \vec{\mu}$, which will vanish if $\vec{\mu}$ is either parallel or anti-parallel with $\vec{B}$, however only one of these configurations will be stable. In the stable configuration, $\vec{\mu}$ will be in the same direction as $\vec{B}$, and if you look at the Lorentz force on any segment of the wire it will be directed outward.

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