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What Is an Electroscope?

By Raine Black
Updated Feb 28, 2024
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An electroscope is a piece of scientific equipment that can measure electrical or in some cases radioactive charges within a target object. While the tool is still frequently used in science labs, its use is primarily instructional — the most common place to find it today is in a school or university. Modern researchers typically use more advanced tools, often digitally driven, that are faster and tend to be more precise. Old-fashioned or early electroscopes are often valued as instructional tools because of how easily they can be observed working. They are usually constructed of a metal material, which enables an electric charge to spread throughout the surface of the instrument. This is often accomplished through induction, which means to make an item have a positive or negative charge without touching it to another already charged object. The two most common variations use either a pith ball or a gold leaf for inflection and induction, but historically there have been many different models.

Main Goal

There are a couple of reasons why people, particularly scientific researchers, want to know about the electrical charges within a given substance. Electrical charge occurs at the atomic level, and influences many of the ways in which different substances act either on their own or in combination with other materials. Electroscopes were developed in large part to enable researchers to determine whether or not a given substance had such a charge.

In most cases 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. Models of all varieties usually have 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.

Earliest Models

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.

The gold leaf modification was invented by clergyman and scientist Abraham Bennet. His device was comprised of two narrow gold leaves hanging from a rod and 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.

Role in Measuring Radioactivity

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.

More Modern Examples

Electroscopes are often regarded as items of curiosity and antiquity. Many are in excellent shape despite being hundreds of years old, and are still capable of producing accurate results; as technology has advanced, though, so have means of measuring electrical charge, which means that electroscopes aren’t really used anymore, at least not as a means of determining charge initially. More often, these tasks are delegated to the related but more advanced electrometers, many of which are digital and able to provide immediate and much more precise results. Many are also able to transmit readings and findings electronically.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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