---
title: "A thin, flat, nonconducting disk of radius \\(R\\) lies in the \\(xy\\)-plane with its center at the origin. A total positive charge \\(Q\\) is distributed uniformly over the surface of the disk. Which of the following expressions correctly gives the electric potential \\(V(z)\\) along the positive \\(z\\)-axis at a distance \\(z\\) from the center of the disk, relative to zero potential at infinity?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/118060/"
date_modified: "2026-08-04T08:04:56+00:00"
---

# A thin, flat, nonconducting disk of radius \(R\) lies in the \(xy\)-plane with its center at the origin. A total positive charge \(Q\) is distributed uniformly over the surface of the disk. Which of the following expressions correctly gives the electric potential \(V(z)\) along the positive \(z\)-axis at a distance \(z\) from the center of the disk, relative to zero potential at infinity?

A thin, flat, nonconducting disk of radius \(R\) lies in the \(xy\)-plane with its center at the origin. A total positive charge \(Q\) is distributed uniformly over the surface of the disk. Which of the following expressions correctly gives the electric potential \(V(z)\) along the positive \(z\)-axis at a distance \(z\) from the center of the disk, relative to zero potential at infinity?

![A thin flat disk of radius R lies flat in the xy-plane, centered at the origin. A vertical z-axis passes perpendicularly through the center of the disk. A point P is marked on the positive z-axis at a distance z above the origin. A thin concentric ring element of radius r and width dr is shown on the disk surface. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785830696-08T7Uq.jpg)

- **A.** \(\dfrac{Q}{4\pi\varepsilon_0 \sqrt{R^2 + z^2}}\)
- **B.** \(\dfrac{Q}{4\pi\varepsilon_0 R^2} \left( \sqrt{R^2 + z^2} - z \right)\)
- **C.** \(\dfrac{Q}{2\pi\varepsilon_0 R^2} \left( \sqrt{R^2 + z^2} - z \right)\)
- **D.** \(\dfrac{Q}{2\pi\varepsilon_0 R^2} \sqrt{R^2 + z^2}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/118060/*