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| Elementary charge | |
|---|---|
Common symbols | |
| SI unit | coulomb |
| Dimension | |
| Value | 1.602176634×10−19 C[1] |
The elementary charge, usually denoted by e, is a fundamental physical constant, defined as the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e.[2][a]
In the SI system of units, the value of the elementary charge is exactly defined as = 1.602176634×10−19 coulombs, or 160.2176634 zeptocoulombs (zC).[3] Since the 2019 redefinition of SI base units, the seven SI base units are defined by seven fundamental physical constants, of which the elementary charge is one.
In the centimetre–gram–second system of units (CGS), the corresponding quantity is 4.8032047...×10−10 statcoulombs.[b]
Robert A. Millikan and Harvey Fletcher's oil drop experiment first directly measured the magnitude of the elementary charge in 1909, differing from the modern accepted value by just 0.6%.[4][5] Under assumptions of the then-disputed atomic theory, the elementary charge had also been indirectly inferred to ~3% accuracy from blackbody spectra by Max Planck in 1901[6] and (through the Faraday constant) at order-of-magnitude accuracy by Johann Loschmidt's measurement of the Avogadro number in 1865.
- ^ "2018 CODATA Value: elementary charge". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-05-20.
- ^ International Bureau of Weights and Measures (20 May 2019), The International System of Units (SI) (PDF) (9th ed.), ISBN 978-92-822-2272-0, archived from the original on 18 October 2021
- ^ Newell, David B.; Tiesinga, Eite (2019). The International System of Units (SI). NIST Special Publication 330. Gaithersburg, Maryland: National Institute of Standards and Technology. doi:10.6028/nist.sp.330-2019. S2CID 242934226.
- ^ Millikan, R. A. (1910). "The isolation of an ion, a precision measurement of its charge, and the correction of Stokes's law". Science. 32 (822): 436–448. doi:10.1126/science.32.822.436.
- ^ Fletcher, Harvey (1982). "My work with Millikan on the oil-drop experiment". Physics Today. 35 (6): 43–47. doi:10.1063/1.2915126.
- ^ Klein, Martin J. (1 October 1961). "Max Planck and the beginnings of the quantum theory". Archive for History of Exact Sciences. 1 (5): 459–479. doi:10.1007/BF00327765. ISSN 1432-0657. S2CID 121189755.
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