Parallel Plate Capacitor
Capacitor Charge, Plate Separation, and Voltage
A capacitor is used to store electric charge. The more voltage (electrical pressure) you apply to
the capacitor, the more charge is forced into the capacitor. Also, the more capacitance the
capacitor possesses, the more a given voltage will force in more charge. This relation is
described by the formula q=CV, where q is the charge stored, C is the capacitance, and V is the
voltage applied.
Looking at this formula, one might ask what would happen if charge were kept constant and the
capacitance were varied. The answer is, of course, that the voltage will change! That is what you
will do in this lab.
The Lab Capacitor
A parallel plate capacitor is a device used to study capacitors. It reduces to barest form the
function of a capacitor. Real-world capacitors are usually wrapped up in spirals in small
packages, so the parallel-plate capacitor makes it much easier to relate the function to the device.
This capacitor works by building up opposite charges on parallel plates when a voltage is applied
from one plate to the other. The amount of charge that moves into the plates depends upon the
capacitance and the applied voltage according to the formula Q=CV, where Q is the charge in
Coulombs, C is the capacitance in Farads, and V is the potential difference between the plates in
volts.
Capacitors store energy
If a voltage is applied to a capacitor and then disconnected, the charge that is stored in the
capacitor remains until the capacitor is discharged in some way. An electric field then exists
between the plates, which allow the capacitor to store energy. This is one of the useful aspects of
capacitors, the ability to store energy in an electric field so that can be utilized later on.
What determines the capacitance?
The surface area of the plates and the spacing between them determines the amount of charge that
may be stored per volt applied. The larger the plates and the more closely they are spaced, the
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Voltage
Source
Capacitor with
charges
