If I take a magnet and a superconductor than it will expel the magnetic field lines of the magnet. now if there is a coil of wire on the other side of the superconductor and i start to warm up the superconductor then the magnetic field lines will start passing through superconductor and as well as through the coil. consequently, there will be flux change in the coil and a voltage will be generated. but here, no matter whatever amount of current flows in the coil we do not have to provide additional work because the magnetic flux changes only due to lost of superconductivity. thus we can amplify the current and hence the power output of the coil.

Doesn't this violates the energy conservation law?

  • $\begingroup$ Are you considering also the energy used to warm up the superconductor? That's part of the experiment you pose $\endgroup$
    – docscience
    Commented Oct 22, 2015 at 19:13
  • $\begingroup$ Please change the title to an explicit one. $\endgroup$
    – FraSchelle
    Commented Oct 23, 2015 at 8:03

1 Answer 1


The energy comes from the magnetic energy of the superconductor. Electromagnet is a seat of available energy, much like charged capacitor or Volta's cell is.

  • $\begingroup$ Here , the superconductor only expells the magnetic field due to quantum phenomenon, however we do not provide any work to superconductor for expelling magnetic field . then how does the The energy come from the magnetic energy of the superconductor ? $\endgroup$ Commented Jun 11, 2016 at 16:52
  • $\begingroup$ @HemalPansuriya, getting a piece of magnet or electromagnet closer to the superconductor requires work and is accompanied with superconductor acquiring electric current. The work done in setting up the system gets stored in the system and its surroundings and is released when the superconducting state is destroyed. $\endgroup$ Commented Jun 11, 2016 at 17:25
  • $\begingroup$ but we can put together (magnet and superconductor ) before cooling the superconductor. So, we do not have to worry about getting a magnet closer to superconductor because it not in superconducting state. Then we cool it to its critical temperature and the magnetic lines will be expelled(Misener effect) . Then just bit higher the critical temperature the superconductivity will be lost. Here, the energy we have given is just the temperature difference (just above critical temp. - critical temp.). But, magnetic field will pass through superconductor (and also coil) . $\endgroup$ Commented Jun 12, 2016 at 18:36
  • $\begingroup$ @HemalPansuriya, in that case the energy for setting up the current in the coil is obtained from the energy of the superconductor. By cooling the superconduction-capable material, energy is sucked out of it as heat. Possibly part of its energy is sucked out as EM energy and stored in the magnetic field of the coil. $\endgroup$ Commented Jun 22, 2016 at 19:28
  • $\begingroup$ here, energy input is proportional to the temperature difference (between cooling and heating) . whereas energy output from coil is arbitrary. we can draw arbitrary large current from the coil since it wont affect energy input (which is fixed and proportional to temperature difference) . and hence here the energy input and output is not equal.If we draw current such that energy output is more than input, then energy conservation will be violated. and here we dont have to worry about lenz's law, because both magnet and coil are kept fixed and hence there is no movement. $\endgroup$ Commented Dec 22, 2016 at 4:14

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