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Feb14-12, 09:59 AM
P: 17,526
Quote Quote by universal_101 View Post
But there should be all these effects when the current is ON, that is, when electrons are moving and therefore there should be length contraction and thus Force.
Yes, when the current is ON then the electrons and the test charge are moving, all these effects are present, and there is a force.

In the lab frame the force is attributed to the magnetic force on the moving charge due to the current in the neutral wire. In the electron/test-charge frame the force is attributed to the electrostatic force on the stationary charge due to the net charge in the wire.