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Value electron mass - electron rest mass
In some experiments, the charge-to-mass ratio is the only quantity that can be measured directly. Often, the charge can be inferred from theoretical considerations, so that the charge-to-mass ratio provides a way to calculate the mass of a particle.
The electron charge to mass quotient, e/m, is a quantity in experimental physics. It matters because the electron mass m is difficult to measure directly, and is instead derived from measurements of the fundamental charge e and e/m. It also has historical significance: Thomson's measurement of e/m convinced him that cathode rays were particles, which we know as electrons.
The 2006 CODATA recommended value is: e/m = 1.758820150(44) C/kg.
In 1897 J. J. Thomson, an English physicist, conducted a series of experiments on cathode rays. As a result of his experiments, Thomson was able to measure the charge to mass ratio of the electron; he could not however, measure accurately the charge or mass independently. The measurement of the electron's charge independently was achieved by Millikan by his famous experiment from 1909 and with Thomson's results also a value for the electron mass was obtained.This experiment is called the oil-drop experiment and it was the first successful scientific attempt to detect and measure the effect of an individual subatomic particle.
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Robert Andrews Millikan was born on the 22nd of March, 1868, in Morrison, Ill. (U.S.A.), as the second son of the Reverend Silas Franklin Millikan and Mary Jane Andrews.
As a scientist, Millikan made numerous momentous discoveries, chiefly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity. Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant h (1912-1915). |
He has been the recipient of the Comstock Prize of the National Academy of Sciences, of the Edison Medal of the American Institute of Electrical Engineers, of the Hughes Medal of the Royal Society of Great Britain, and of the Nobel Prize for Physics 1923.
He died on the 19th of December, 1953, in San Marino, California.
We shall use the next formula to calculate the mass of the electron in Bohr`s atom:
and where are:
Using the best experimental values for r,R,h_bar and (the value of c is fixed by definition) gives:
Now, we shall use the another formula to calculate again the mass of the electron in Bohr`s atom:
where the value of fine structure constant is:
Using the best experimental values for r,R,h_bar and (the value of c is fixed by definition) gives the value electron mass:
Electron mass ( electron rest mass ) is atomic fundamental physical constant used as atomic unit of mass,
m = 9.109 382 15 (45) * 10-31 kg. (CODATA, 2006.)
The 2007 Rasko Jovanovic recommended value is:
See: Planck`s constant and number PI
See: Elementary charge and The Golden Section
See: Fine structure constant and The Golden Section
Kinoshita, T. "The Fine Structure Constant." Rept. Prof. Phys. 59, 1459-1492, 1996.
Planck, M. "Zur Theorie des Gesetzes der Energieverteilung im Normalspektrum." Verhandl. Deutsch. phys. Ges. 2, 237, 1900.
P. A. M. Dirac, Nature 139, 323 (1937)
Dirac, P.A.M. Principles of Quantum Mechanics, 4th ed. Oxford, England: Oxford University Press, 1982.
B.W.Petley: The Fundemental Physical Constants and the Frontier of Measurement" Adam Hilger Ltd. Bristol UK, 1985.
Hans A.Bethe: "Intermediate Quantum Mechanics",W.A.Benjamin Inc,New York - Amsterdam (1964).
Srpska Akademija nauka i umetnosti: "Elektron-sto godina od otkrica",
Zavod za udzbenike i nastavna sredstva, Beograd (1997)
Todorovic,Milan: "Atomska fizika".Elektrotehnicki fakultet, Beograd (1973).
Ivanovic,Dragisa: "Kvantna mehanika".Naucna knjiga, Beograd (1972).
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