25. The disk is uniformly charged. This means that when the full disk is present each quadrant contributes equally to the electric potential at P, so the potential at Pdue to a single quadrant is one-fourth the potential due to the entire disk. First find an expression for the potential at Pdue to the entire disk. We consider a ring of charge with radius rand (infinitesimal) width dr. Its area is 2πr drand it contains charge dq= 2πσr dr. All the charge in it is a distance22rD+from
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