Consider a metallic rod hung by two springs (symmetrically), a magnetic field exists out of the plane of our system. At t = 0, we switch on a battery which produces current in wire (left to right in the rod) so now, a force of magnetic origin acts on the rod to pull it down and extend the springs thus magnetic force appears to do work in this case.

So is the fact that magnetic forces don't do work incorrect? Because I don't think that some other force can do work on the system

Assume the rod and springs to be massless.

  • $\begingroup$ What about the battery pumping charges through the circuit? $\endgroup$ – Jan Bos Sep 12 '16 at 12:24
  • $\begingroup$ All of that work would translate to heat loss only I've tried it, the numbers match up exactly $\endgroup$ – Rishabh Sep 12 '16 at 12:40
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    $\begingroup$ The electrons feel the force of the magnetic field while being accelerated between collisions by the battery's E field providing an average momentum perpendicular to the wire and magnetic field. These collisions with an average side ways momentum causes the springs to stretch so is not all lost in heat. $\endgroup$ – Jan Bos Sep 12 '16 at 14:16
  • $\begingroup$ In the case you explained, still work done by magnetic field won't be zero and that was my question $\endgroup$ – Rishabh Sep 12 '16 at 14:40
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    $\begingroup$ Possible duplicate of Positive work by a magnetic field $\endgroup$ – John Rennie Sep 12 '16 at 15:28