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I heard somewhere that If you add a magnetic field to atoms in a closed space you would speed them up. Similarly to heating them up. Is this true is so what the atom consists of for this to work?

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Case 1 ( Magnetic field is constant)

No, while it can change velocity DIRECTION, it cant change the magnitude of velocity. That is, since force due to magnetic field is always perpendicular to direction of propogation, we infer that the speed of a moving charged particle always remains constant in a magnetic field.

Case 2 (Varying magnetic field)

Situation is different in a varying magnetic field. A varying magnetic field produces an induced electric field(which forms closed loops and are NOT CONSERVATIVE).Thus the electric field produced due to varying magnetic field change the speed. However due to motion of charged particle, it also experiences magnetic force perpendicular to direction of propogation

Conclusion:-

We conclude that magnetic FIELD MAY change the speed. However I would add that magnetic FORCE can never change SPEED(but can change velocity).

ps- emphasis on words FIELD and FORCE. Also, it is assumed that propogation is orthogonal to direction of Magnetic field.

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    $\begingroup$ If you turn a magnetic field on adiabatically, you are restricting the motion from three dimensions to two, which changes the velocity (and temperature). This is being used quite ingeniously in magnetic refrigeration: en.wikipedia.org/wiki/Magnetic_refrigeration $\endgroup$ – CuriousOne May 28 '16 at 23:20
  • $\begingroup$ I think it's a wonderful technique that one should have heard about. I do agree with your answer by the way. It answers the question on the right level of understanding and for the non-thermodynamic case, that's just not the entire bandwidth of phenomena that nature can throw at us and it's good to be aware of what happens when the atoms/molecules/spins are not free but coupled to temperature baths. $\endgroup$ – CuriousOne May 28 '16 at 23:36

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