View source for Elementary charge



The '''elementary charge''', e, is the [[electric charge]] carried by a single [[proton]], or equivalently, the negative of the '''electric charge''' carried by a single [[electron]].

This is a fundamental [[physical constant]] and the [[Units of measurement|unit]] of '''electric charge''' in the system of [[atomic units]] as well as some other systems of [[natural units]].

It has a measured value of approximately {{val|1.602176487|e=-19|ul=C}}, according to the [[NIST]] posted [http://physics.nist.gov/cgi-bin/cuu/Value?e CODATA value for ''e'']. See the 2006 Committee on Data for Science and Technology (CODATA) list of physical constants: [http://physics.nist.gov/cuu/Constants/codata.pdf CODATA report, TABLE XLVIII] for uncertainty in ''e''.  In the [[centimetre gram second system of units]], the value is {{nowrap|{{val|4.803204273|e=-10}} [[statcoulomb]]s}}.

Since it was first measured in [[Robert Andrews Millikan|Robert Millikan]]'s famous [[oil-drop experiment]] in 1909, the elementary charge has been considered indivisible.  [[Quark]]s, first posited in the 1960s, have fractional electric charges (in units of {{frac|1|3}}&thinsp;''e'' and {{frac|2|3}}&thinsp;''e'' so that now the term ''elementary charge'' referring to the charge on an electron is no longer strictly correct; this is irrelevant, however, in practical terms, since quarks are not detected except in groupings that have charges that are integer multiples of e.  In [[1982]] [[Robert B. Laughlin|Robert Laughlin]] tried to explain the fractional [[quantum Hall effect]] by predicting the existence of fractionally charged [[quasiparticle]]s. In [[1995]], the fractional charge of Laughlin quasiparticles was measured directly in a quantum antidot electrometer at [[State University of New York at Stony Brook|Stony Brook University]], [[New York]].  In 1997, two groups of physicists at the [[Weizmann Institute of Science]] in [[Rehovot]], [[Israel]], and at the [[Commissariat à l'énergie atomique]] laboratory near [[Paris]], claimed to have detected such quasiparticles carrying an [[electric current]].

==External links==
*[http://www.jstor.org/view/00368075/di002303/00p0036t/0?currentResult=00368075%2bdi002303%2b00p0036t%2b0%2c01%2b19950217%2b9993%2b80049782&searchID=8dd55340.10818876572&frame=noframe&sortOrder=SCORE&userID=81313876@sunysb.edu/018dd55340005010fc7d6&dpi=3&viewContent=Article&config=jstor "Measurement of fractional charge" (Science Report) 1995]
*[http://quantum.physics.sunysb.edu/index.html "Quantum antidot electrometer"]
*[http://physicsweb.org/article/news/1/10/7/1 "Fractional charge carriers discovered" - Physics Web article 1997-10-24]
*[http://www.nature.com/cgi-taf/google_referrer.taf?article_product_code=NATURE&fulltext_filename=/nature/journal/v389/n6647/full/389162a0_fs.html&_UserReference=C0A804F846B4FE09B530543FD0523FA3D356 "Direct observation of a fractional charge" (letter to Nature) 1997]

==References==
'''Fundamentals of Physics''', 7th Ed., Halliday, Robert Resnick, and Jearl Walker. Wiley, 2005

[[Category:Physical constants]]
[[Category:Units of electrical charge]]

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