# Wire in an E field?

by cragar
Tags: field, wire
 P: 2,444 If I had a current carrying wire in an E field. Would it deflect? The wire it self just has a B field and no free charge. But If I was moving with respect to the wire I would see length contraction and a net E field. So in my frame the wire would deflect. Or is something wrong with my reasoning?
HW Helper
P: 4,523
 Quote by cragar If I had a current carrying wire in an E field. Would it deflect?
I expect it wouldn't. But let's make it more interesting, and use a length of resistance wire so there is significant potential across the wire. (Make it of carbon and delicately suspend it with elastic quartz fibres to avoid arguments.) Would it experience deflecting forces now with a few hundred volts P.D.?
 But If I was moving with respect to the wire I would see length contraction and a net E field. So in my frame the wire would deflect. Or is something wrong with my reasoning?
I can't comment.
 P: 2,444 so if we have a suspended wire with a voltage across it, so There is an E field down the wire, so it is basically like a plate capacitor. So if we have a charge separation in the wire the +q and -q charged will experience forces in the opposite directions and should cancel.
HW Helper
P: 4,523

## Wire in an E field?

 Quote by cragar so if we have a suspended wire with a voltage across it, so There is an E field down the wire, so it is basically like a plate capacitor. So if we have a charge separation in the wire the +q and -q charged will experience forces in the opposite directions and should cancel.
I think the more positive end of the wire will be pushed by the E field (i.e., attracted towards the negative plate) and the negative end of the wire will be attracted by the E field (i.e., attracted towards the positive plate), so the wire will tend to rotate about an axis through its centre.
 P: 2,444 So torque on an Electric dipole.
 P: 2,444 Now that I think more about my original post, an looking at this in the moving frame. If I move with respect to this wire an I get a net E field from the wire, I will also get a B field from the external E field, and this will cause a Lorentz force F= q(vxB) and this will probably balance the F=qE from the E field.

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