# Do we measure a voltage across a conductor moving at a constant velocity in a uniform magnetic field with a moving voltmeter?

Image courtesy of @Alfred Centauri from Is there an EMF in a conductor moving at constant speed across the uniform magnetic field This is what we observe from the rest frame. But were we in the frame of the conductor i.e. the voltmeter were attached to either end of the rod and moving with it, would it detect a voltage?

I guess even from the rest frame looking at the voltmeter we would see zero voltage, because now there is a closed loop of wire moving through the uniform magnetic field (closed by the voltmeter) at constant speed.

So then the only way we could really observe a voltage on the voltmeter would be to have a stationary (relative to us) voltmeter consisting of two rails on which the bar slides (like a rail gun) --> law of induction

Is that so? It would seem in some ways disappointing, in others interesting. Sorry for my naivite I am in no way a physicist!

• Your picture does not match your scenario. The picture doesn't show a closed circuit. Aug 9, 2018 at 10:18