Consider a simple electrical circuit made up of a battery, an incandescent bulb, and wire. The battery and bulb are equal in mass and are on opposite sides of a circle made up by the wire. Lastly, the circuit is operating and floating freely in microgravity.

Since an electromotive force propels objects with mass (electrons) around the circuit, can we expect the circuit, given enough battery life, to eventually rotate in the opposite direction of the electrons due to Newton’s third law of motion?

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    $\begingroup$ An early effort to detect this effect was made by Einstein and de Haas, but since electron spin had not been discovered yet, their prediction was doomed to be wrong. The story is well-told by Galison in his How Experiments End. $\endgroup$ – rob Mar 15 at 0:37
  • $\begingroup$ You ask if current creates acceleration. An alternate answer refers to how acceleration creates current. physics.stackexchange.com/a/397315/55662 $\endgroup$ – BowlOfRed Mar 15 at 6:34

Yes, conservation of angular momentum applies and the system will not rotate. I assume that the bulb radiates isotropically and also that any other radiation effects are isotropic. The electrons cannot be set into motion without a reaction force on the battery. However the magnetic field will polarise electron spins, free or located in ferromagnetic atoms. This will align their spin angular momentum possibly causing an undoubtedly tiny opposite angular momentum of the setup.

  • $\begingroup$ I wish there were a third option besides upvote and downvote which would be a big question mark. $\endgroup$ – DWin Mar 16 at 1:40
  • $\begingroup$ @DWin Check your keyboard again. $\endgroup$ – my2cts Mar 16 at 6:46

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