A disk of radius \(R\) has positive charge uniformly distributed over an inner circular region of radius \(a\) and negative charge uniformly distributed over the outer annular (ring-shaped) region (Figure P25.56). The surface charge density on the inner region is \(+\sigma\), and that on the annular region is \(-\sigma\). The electrostatic potential at \(\mathrm{P}\), located on the central perpendicular axis a distance \(z=R\) from the disk center, is zero. What is \(a\) in terms of \(R\) ?

Data from Figure P25.56

Transcribed Image Text:

Figure P25.56 x z=R 4+ R x