---
title: "A parallel-plate capacitor consists of two flat conducting plates separated by a small air gap. When the capacitor is charged, a uniform electric field \\(\\vec{E}\\) is established in the region far from the edges of the plates. Which of the following best explains why the electric field in electrostatic equilibrium must be perpendicular to the surfaces of the conducting plates?"
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url: "https://nerd-notes.com/ubq/117019/"
date_modified: "2026-08-04T06:17:00+00:00"
---

# A parallel-plate capacitor consists of two flat conducting plates separated by a small air gap. When the capacitor is charged, a uniform electric field \(\vec{E}\) is established in the region far from the edges of the plates. Which of the following best explains why the electric field in electrostatic equilibrium must be perpendicular to the surfaces of the conducting plates?

A parallel-plate capacitor consists of two flat conducting plates separated by a small air gap. When the capacitor is charged, a uniform electric field \(\vec{E}\) is established in the region far from the edges of the plates. Which of the following best explains why the electric field in electrostatic equilibrium must be perpendicular to the surfaces of the conducting plates?

![A side-view diagram of a parallel-plate capacitor oriented horizontally. Two thin horizontal rectangular plates of equal length are separated by a small vertical gap and positioned parallel to each other. The upper plate is drawn as a dark horizontal line with five positive sign labels '+' placed at equal intervals along its upper surface. The lower plate is drawn as a dark horizontal line with five negative sign labels '-' placed at equal intervals along its lower surface. In the interior space between the two plates, four parallel straight vertical vector arrows point straight down from the upper plate to the lower plate. These arrows are evenly spaced across the middle region and are labeled with the electric field vector symbol '\vec{E}'. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785824220-0v5P80.jpg)

- **A.** The electric field is perpendicular to the plates because charges on opposing plates attract each other directly across the gap, which prevents any force from acting parallel to the plate surfaces.
- **B.** The electric field is perpendicular to the plates because the magnetic force from static surface charges cancels any component of the electric field that is parallel to the plates.
- **C.** The electric field is perpendicular to the plates because any parallel field component would exert forces on free electrons, causing charge to flow along the plates until electrostatic equilibrium is reached and the parallel field becomes zero.
- **D.** The electric field is perpendicular to the plates because electric field lines are always parallel to equipotential surfaces in the region between the plates.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117019/*