When a charged disc is rotated about it's axis does it exert torque on itself?
It seemed logical enough as there is magnetic feild associated with the spin of disc has force on it but I didn't find any way to calculate that feild at parts other than the center of the disc. Is there any logical way of approaching it.
If there was net torque then a charged disc kept in isolation must get retarded and ultimately stop but this may bring violations in energy conservation.
Could someone explain where my approach is wrong.

  • $\begingroup$ what direction will the magnetic field have? What direction should a torque have? "A magnetic field has force" is a very obscure statemnent. Force on what? $\endgroup$
    – trula
    Sep 18, 2020 at 19:36

1 Answer 1


No, it definitely wouldn't exert a torque on itself. If you apply Biot Savart's law and the Lorentz Force correctly, you will see that there is a compressive force on the disc.

Also, in other cases, when magnetic force causes a moving current carrying element to retard and finally stop, energy is still conserved, as the resistance of the current carrying element produces heat.


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