56. (a) The period of rotation is T =2 π/ω and in this time all the charge passes any Fxed point near the ring. The average current is i = q/T = qω/ 2 π and the magnitude of the magnetic dipole moment is µ = iA = qω 2 π πr 2 = 1 2 qωr 2 . (b) We curl the Fngers of our right hand in the direction of rotation. Since the charge is positive, the
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