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# Electric Fields

## Electric fields are used to keep track of forces that charged particles feel.

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Storing Static Electricity

### Storing Static Electricity

Credit: Walter Larden
Source: http://commons.wikimedia.org/wiki/File:Leyden_jar_cutaway.png

The Leyden jar was created in 1745 in order to store static electricity during some of the earliest experiments on electricity.

#### News You Can Use

• A Leyden jar consists of a glass jar that has a conducting foil (such as aluminum) that coats the inner and outer surface. A metal rod is held in place and inserted through a stopper at the top of the jar and placed so that it is in contact with the inner surface of the jar. The rod allows the inner surface to be electrically charged when the metal rod is touched with an external electric charge.
• Because it can store electrical charge, the Leyden jar serves as a basic form of a capacitor. A capacitor is a system in which two conductors (objects capable of transferring electric charge) carry equal but opposite charge. The capacitance of a typical Leyden jar is approximately 1 nano-Farad (nF). Farad (F) is the basic unit of capacitance. Capacitance (C\begin{align*}C\end{align*}) is defined as the charge of the plate (Q\begin{align*}Q\end{align*}) divided by the potential difference, or voltage, between the two conductors (V\begin{align*}V\end{align*}):

C=QV\begin{align*}C=\frac{Q}{V}\end{align*}

#### Show What You Know

1. Why is the gold leaf attracted to the hands of the person laying on the swings in the video?
2. If 88 pF capacitor is charged to 12 V, how much charge is transferred from one plate to another?
3. Given that the stored static electricity is evenly distributed across the inner foil, would you expect the electric field between the two foil surfaces (inner and outer) to be uniform or non-uniform?

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