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scotshocker
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Homework Statement
A thin copper (resistivity 1.7 x 10-8 Ωm, density 8.9 g/cm3) ring rotates about an axis perpendicular to a uniform magnetic field B0. Its initial frequency of rotation is ω0. Calculate the time it takes the frequency to decrease to 1/e of its initial value, under the assumption that the energy goes into joule heat, if the magnitude of the field is 0.002 T.
Homework Equations
The Attempt at a Solution
I had found a version similar to this but unfortunately when I try to convert it into SI units the units do not work out.
Kinetic Energy of rotation:=.5Izω2
Iz=.5Mr^2 M=2πArρ Iz=πAr3ρ
r= radius A=cross section ρ=mass density
magnetic flux [itex]\Phi[/itex] = B0r2πcos(Θ)
Θ= angle between field and plane of the ring
rotation Θ=ωt
Lenz's law: V=[itex]\frac{d\phi }{dt}[/itex] r2πB0ωsin(ωt)
The rest can be found here but as I said when I convert into SI I am not ending up with the correct units( the problem in question uses different numbers): http://www.physics.fsu.edu/QualifyingExam/Spring07_solutions.pdf Solution 10
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