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What Is an Electroscope?

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  • Written By: Raine Black
  • Edited By: C. Wilborn
  • Last Modified Date: 25 August 2014
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An electroscope is an early scientific instrument used to determine if a charge is present in an object. It is usually constructed of a metal material, which enables an electric charge to spread throughout the surface of the instrument. This can be done by induction, which means to make an item have a positive or negative charge without touching it to another already charged object. Electroscopes are not capable of telling whether a charge is positive or negative; they are only able to convey information about how much of a charge is present.

This tool usually has turning arms that reveal whether or not a there is a charge present. The arms may remain vertical if there is no charge present, moving when the machine receives a charge. Movement of the arms can also be affected by items in the vicinity that contain a charge.

In the 1700s, physicist and clergyman Jean Antoine Nollet devised the first electroscope. He also formulated a theory on charged bodies, and how a sustained electricity current between them can cause them to either attract or repel. The instrument was advancement in design on the versorium, a device to detect static electricity.

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The gold leaf electroscope was invented by clergyman and scientist Abraham Bennet. His device was comprised of the narrow gold leaves hanging from a rod, surrounded by glass. When anything with electricity flowing through it came near the rod, the leaves would move. If they were electrified with the same amount of charge, they would repel away from each other.

One of the most innovative uses of the electroscope came about in the 1800s under researchers Marie and Pierre Curie. Very sophisticated versions of the instrument were used by these researchers to examine radioactivity. Radioactive materials ionize a substance within the charged electroscope. The ionizing that takes place causes the charge to escape from the device more quickly than it normally would. The rate at which the tool loses its charge is then measured, and this rate is proportional to the radiation intensity.

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