It has a measured value of approximately 176487×10−19 C, according to the 1.602NIST posted CODATA value for e. See the 2006 Committee on Data for Science and Technology (CODATA) list of physical constants: CODATA report, TABLE XLVIII for uncertainty in e. In the centimetre gram second system of units, the value is 204273×10−10 4.803statcoulombs.
Since it was first measured in Robert Millikan's famous oil-drop experiment in 1909, the elementary charge has been considered indivisible. Quarks, first posited in the 1960s, have fractional electric charges (in units of 1⁄3 e and 2⁄3 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 Laughlin tried to explain the fractional quantum Hall effect by predicting the existence of fractionally charged quasiparticles. In 1995, the fractional charge of Laughlin quasiparticles was measured directly in a quantum antidot electrometer at 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.
- "Measurement of fractional charge" (Science Report) 1995
- "Quantum antidot electrometer"
- "Fractional charge carriers discovered" - Physics Web article 1997-10-24
- "Direct observation of a fractional charge" (letter to Nature) 1997
Fundamentals of Physics, 7th Ed., Halliday, Robert Resnick, and Jearl Walker. Wiley, 2005
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