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cromata
Homework Statement
A metal disc of radius R rotates with a constant velocity ω about its axis. FInd the potential difference between the centre and the rim of the disc if:
a)the external magnetic field is absent
b)the external magnetic field of induction B is directed perpendicular to the disc
c)Why is there a difference between results in those two cases if rotE=0 for consant magnetic field (3rd Maxwell equation).
Homework Equations
Δφ=∫Edr
Fmag=qv×B
The Attempt at a Solution
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.
b)I think this question is undefined because it's not same if B and ω are parallel or antiparallel. Let's suppose that they are parallel, then magnetic force on electron is F=Beωr (directed to the centre of the disc), so we have Fcp=B+E, and from here we can calculate E and then use Δφ=∫Edr... but i think i got something wrong in this b)part and i don't know the answer on last question