Question

A conducting disc of radius r is placed in a uniform and constant magnetic field b parallel to the axis of the disc. With what angular speed should the disc be rotated about its axis such that no electric field develops in the disc.( the electronic charge and mass are e and m)

Answer 1

a)Free electrons of metal disc are rotating, so there has to be some force that is responsible for centripetal acceleration of electrons. That force exists because free electrons go to the rim of the disc and create electric field, so we have: Fcp=e*E, E=m*ω^2*r/e. So potential diference is Δφ=∫Edr (from 0 to R), Δφ=mω^2*r^2/2e.

Reference

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