A thin disk of radius \(R=5 \mathrm{~cm}\) has uniform surface charge density \(\sigma=8 \mathrm{nC} / \mathrm{m}^{2}\). Calculate the potential (relative to zero at infinity) on the axis that runs through the disk center and is perpendicular to the disk face at distances

(a)  \(5.0 \mathrm{~mm},\)

(b) \(2 \mathrm{~cm}\),

(c) \(1 \mathrm{~m}\).