---
title: "A rectangular dielectric slab of dielectric constant \\(\\kappa > 1\\) is partially inserted a distance \\(x\\) into a parallel-plate capacitor. The capacitor is connected to a battery that maintains a constant potential difference \\(V_0\\) across the plates, and the slab is free to slide horizontally without friction. Which of the following claims correctly describes the direction of the electrostatic force exerted on the slab by the capacitor and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/118242/"
date_modified: "2026-08-04T08:08:23+00:00"
---

# A rectangular dielectric slab of dielectric constant \(\kappa > 1\) is partially inserted a distance \(x\) into a parallel-plate capacitor. The capacitor is connected to a battery that maintains a constant potential difference \(V_0\) across the plates, and the slab is free to slide horizontally without friction. Which of the following claims correctly describes the direction of the electrostatic force exerted on the slab by the capacitor and provides the correct justification?

A rectangular dielectric slab of dielectric constant \(\kappa > 1\) is partially inserted a distance \(x\) into a parallel-plate capacitor. The capacitor is connected to a battery that maintains a constant potential difference \(V_0\) across the plates, and the slab is free to slide horizontally without friction. Which of the following claims correctly describes the direction of the electrostatic force exerted on the slab by the capacitor and provides the correct justification?

![A schematic diagram showing a parallel-plate capacitor with two horizontal parallel conducting plates connected to a battery symbol supplying potential difference V_0. A rectangular dielectric slab of dielectric constant \kappa is partially inserted from the left between the plates along the x-axis. A distance x represents the length of the slab currently inside the capacitor plates. Arrow labeled x points along the horizontal direction of insertion toward the interior of the capacitor. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785830903-Uy9boM.jpg)

- **A.** The dielectric experiences an outward force, because inserting the slab increases the stored electrostatic energy of the capacitor, and physical systems naturally move toward lower potential energy states.
- **B.** The dielectric experiences an inward force, because inserting the slab increases the capacitance, and at constant potential difference, the electrostatic force is given by \(F = \dfrac{1}{2}V_0^2 \dfrac{dC}{dx} > 0\).
- **C.** The dielectric experiences an inward force, because inserting the slab decreases the stored electrostatic energy of the capacitor, and the electrostatic force acts in the direction that decreases stored energy.
- **D.** The dielectric experiences an outward force, because the bound surface charge induced on the dielectric is repelled by the free charge on the capacitor plates.

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