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Question 5.6: (a) A phonograph record carries a uniform density of “static...

(a) A phonograph record carries a uniform density of “static electricity” σ. If it rotates at angular velocity ω, what is the surface current density K at a distance r from the center?

(b) A uniformly charged solid sphere, of radius R and total charge Q, is centered at the origin and spinning at a constant angular velocity ω about the z axis. Find the current density J at any point (r, \theta, \phi) within the sphere. 

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