### Introduction

A capacitor is defined as any two conductors, separated by an insulator where each conductor carries a net excess charge that is equal in magnitude and opposite in sign. Its capacitance, C, is defined as

$C \equiv \frac{Q} {V}$

where Q is the magnitude of the excess charge on each conductor and V is the voltage (or potential difference) across the plates.

We can use Gauss’ Law to analyze a parallel plate capacitor if we assume that most of the electric field lines are perpendicular to the plates. According to Gauss, if air is the insulator, the capacitance, C, is related to the area of the plates, A, and the spacing between them, d, by the equation

$C = \frac{{{\varepsilon _0}A}} {d}$

ε0 is known as the electric constant (or permittivity).

### Objectives

In this activity, you will

• Explore how the voltage (a.k.a. potential difference) across the plates varies as the distance between the charged plates increases.