222 Faraday’s Law*P31.24Observe that the homopolar generator has no commutator andproduces a voltage constant in time: DC with no ripple. In time dt, thedisk turns by angle ddtθω=. The outer brush slides over distance rdθ.The radial line to the outer brush sweeps over areadArrdrdt==12122.The emf generated isε=−⋅NddtBAεω°FHGIKJ10122afBdAdtBrcos(We could think of this as following from the result of Example 31.4.)The magnitude of the emf isFIG. P31.24π=FHGIKJ=⋅⋅LNMOQPFHGIKJ=12091204320026024122...NsCmmrevminrad revsmVbgafA free positive charge qshown, turning with the disk, feels a magnetic force qvB×radiallyoutward. Thus the outer contact is positive .*P31.25The speed of waves on the wire isvT⋅×=−µ2672983Nm310 kgms.In the simplest standing-wave vibration state,dNN0642. mλ=128mand fv
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Magnetic Field, Trigraph, Faraday's law of induction, rad rev IJ, outer brush