Editing Electrometer (section)

=== Gold-leaf electroscope ===
[[Image:Electroscope.png|thumb|200px|upright|Gold-leaf electroscope]]
{{main|electroscope}}
The gold-leaf electroscope was one of the instruments used to indicate electric charge.<ref name=EB1911/> It is still used for science demonstrations but has been superseded in most applications by electronic measuring instruments. The instrument consists of two thin leaves of gold foil suspended from an [[electrode]]. When the electrode is charged by [[electrostatic induction|induction]] or by contact, the leaves acquire similar electric charges and repel each other due to the [[Coulomb force]]. Their separation is a direct indication of the net charge stored on them. On the glass opposite the leaves, pieces of tin foil may be pasted, so that when the leaves diverge fully they may discharge into the ground. The leaves may be enclosed in a glass envelope to protect them from drafts, and the envelope may be [[vacuum|evacuated]] to minimize charge leakage. This principle has been used to detect ionizing radiation, as seen in the [[Quartz fiber dosimeter|quartz fibre electrometer]] and [[Kearny fallout meter]].

This type of electroscope usually acts as an indicator and not a measuring device, although it can be calibrated. A calibrated electrometer with a more robust aluminium indicator was invented by [[Ferdinand Braun]] and first described in 1887.  According to Braun, the standard gold-leaf electrometer is good up to about {{nowrap|800 V}} with a resolution of {{nowrap|0.1 V}} using an [[ocular micrometer]].  For larger voltages up to {{nowrap|4–6 kV}} Braun's instrument can achieve a resolution of {{nowrap|10 V}}.<ref>Ferdinand Braun, [https://zenodo.org/record/1757498#.YUicgH3TWUk "Ueber das electrische Verhalten des Steinsalzes"], ''Annalen der Physik'', vol. 31, pp. 855–872, 1887.</ref><ref>[https://www.orau.org/health-physics-museum/collection/electroscopes/electrostatic/braun.html "Braun Electroscope (early 1900s)"], ORAU Museum of Radiation and Radiology, retrieved 20 September 2021.</ref>

The instrument was developed in the 18th century by several researchers, among them [[Abraham Bennet]] (1787)<ref name=Baigrie/> and [[Alessandro Volta]].