A thin, nonconducting disk of radius \(R\) is located in the \(xy\)-plane with its center at the origin. The disk has a uniform surface charge density \(\sigma\). A point \(P\) is located on the \(z\)-axis at a distance \(z\) from the center of the disk. Which of the following expressions correctly represents the electric potential \(V\) at point \(P\), assuming the potential is zero at infinity?