43. A disk of radius a carries uniform surface charge density σand rotates with angular speed ω about the disk axis. What is the magnetic field at the disk center? (μ0 is the magnetic constant.)
(A) μ0σωa
(B)μ0πσa2
(C) μ0πσa2
(D) μ0σωa2
(E) μ0σωa

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統計： A(0), B(1), C(0), D(1), E(1) #3840153