Electroscope

The simplest type of electroscope is the gold-leaf electroscope. This device has two slender strips of gold foil that hang straight down from a metal conductor. A nonconductor, such as cork, holds the conductor in a stand made of glass or metal. If an electrically charged object touches the conductor, the strips become charged. Both strips receive the same kind of charge and, because like charges repel each other, the strips spread apart in an upside-down V.

Gold-leaf and other simple electroscopes have been replaced by more sensitive solid-state electrometers for scientific research. These electronic instruments contain a capacitor, a device that stores an electric charge. When a charged object touches the electrometer's conductor, the charge produces a small voltage in the capacitor. The electrometer electronically amplifies this voltage so its value can be shown on a meter or on an instrument called an oscilloscope (see Oscilloscope).

Many people who work in areas where radiation may be present use an electroscope as a dosimeter. A dosimeter is a device that measures the amount of radiation to which a person has been exposed. An electroscope must be charged before it can be used as a dosimeter. It gradually discharges when exposed to gamma rays, X rays, or other forms of radiation. The amount of charge lost shows the level of exposure.

The first electroscope was made by William Gilbert, the physician of Queen Elizabeth I of England. He described it in a book published in 1600.

Contributor: Robert B. Prigo, Ph.D., Prof. of Physics, Middlebury College.

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