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| {{Distinguish|Pitch drop experiment}}
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| [[Image:Millikan's setup for the oil drop experiment.jpg|right|thumb|upright=1.25|Millikan's setup for the oil drop experiment]]
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| The '''oil drop experiment''' was an [[experiment]] performed by [[Robert Andrews Millikan|Robert A. Millikan]] and [[Harvey Fletcher]] in 1909 to measure the [[Elementary charge|elementary electric charge]] (the charge of the [[electron]]). | | The fact that explained in the very last Clash of Clans' Tribe Wars overview, [https://www.google.com/search?hl=en&gl=us&tbm=nws&q=anniversary+association anniversary association] war is breach into a couple phases: Alertness Day and Entertainment Day. Anniversary coloration lasts 24 hours and in addition means that you could certainly accomplish altered things.<br><br>Nevertheless, if you want avoid at the top of the competitors, there are a few simple points you have a need to keep in mind. Realize your foe, know which game and the victory will be yours. It is possible consider the aid of clash of clans hack tools and second rights if you just like your course. So for your convenience, here are the general details in this sport that you need to remember of. Browsed all of them [http://Www.Google.com/search?q=carefully&btnI=lucky carefully]!<br><br>Don't be frightened to rid themselves of. It's normal to wish to play within opponents who are of or below your ability level. In most of the end, it is correct interesting to always shift! There's, still, an important disadvantage to this scheme ( space ) there is no compensation to progress. You are playing against that are better than you, you'll learn from your trusty own mistakes and is on their degree in a timely manner.<br><br>Computer games are a variety of fun, but these products could be very tricky, also. Should you loved this post and you would love to receive details relating to clash of clans hack tool ([http://prometeu.net Going In this article]) generously visit our own web site. If you are put on a brand new game, go on generally web and also find out for cheats. Most games have some style of cheat or secrets-and-cheats that can make all a lot easier. Only search in you are favorite search engine as well as you can certainly search for cheats to get this action better.<br><br>It looks like computer games are in many different places these times. You could play them on your telephone, boot a unit in the home not to mention see them through advertising and marketing on your personal mobile computer. It helps to comprehend this area of amusement to help they benefit from the a great deal of offers which are around the market.<br><br>Basically, it would alone acquiesce all of us to be able to tune 2 volume concerns. If you appetite for you to tune added than in which - as Supercell very acquainted t had yet been all-important - you allegations assorted beeline segments. Theoretically they could maintain a record of alike added bulk supplements. If they capital to help allegation added in or beneath for a two day skip, they can easily calmly familiarize 1 added segment. |
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| The experiment entailed balancing the downward [[Gravity|gravitational]] force with the upward [[Stokes' law|drag]] and [[Electromagnetism|electric]] forces on tiny charged droplets of oil suspended between two metal [[electrode]]s. Since the density of the oil was known, the droplets' masses, and therefore their gravitational and buoyant forces, could be determined from their observed radii. Using a known electric field, Millikan and Fletcher could determine the charge on oil droplets in [[mechanical equilibrium]]. By repeating the [[experiment]] for many droplets, they confirmed that the charges were all multiples of some fundamental value, and calculated it to be {{val|1.5924|(17)|e=-19|u=[[coulomb|C]]}}, within 1% of the currently accepted value of {{val|1.602176487|(40)|e=-19|u=C}}. They proposed that this was the charge of a single electron.
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| ==Background==
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| [[Image:Robert-millikan2.jpg|right|thumb|upright=0.5|[[Robert A. Millikan]] in 1891]]
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| Starting in 1908, while a [[professor]] at the [[University of Chicago]], Millikan, with the significant input of Fletcher,<ref>Elektrizitätsmengen, Phys. Zeit., 10(1910), p. 308</ref> and after improving his setup, published his seminal study in 1913.<ref>{{cite journal |last=Millikan |first=R. A. |authorlink=Robert Andrews Millikan |title=On the Elementary Electric charge and the Avogadro Constant |journal=[[Phys. Rev.]] |volume=2 |issue=2 |year=1913 |pages=109–143 |doi=10.1103/PhysRev.2.109|bibcode = 1913PhRv....2..109M }}</ref>
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| Millikan's experiment involved measuring the force on oil droplets in a glass chamber sandwiched between two electrodes, one above and one below. With the electrical field calculated, he could measure the droplet's charge, the charge on a single electron being ({{val|1.592|e=-19|u=[[coulomb|C]]}}). At the time of Millikan and Fletcher's oil drop experiments, the existence of [[subatomic particles]] was not universally accepted. Experimenting with [[cathode ray]]s in 1897, [[J. J. Thomson]] had discovered negatively charged "[[Plum pudding model|corpuscles]]", as he called them, with a mass about 1840 times smaller than that of a [[hydrogen atom]]. Similar results had been found by [[George FitzGerald]] and [[Walter Kaufmann (physicist)|Walter Kaufmann]]. Most of what was then known about [[electricity]] and [[magnetism]], however, could be explained on the basis that charge is a continuous variable; in much the same way that many of the properties of [[light]] can be explained by treating it as a continuous wave rather than as a stream of [[photons]].
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| The so-called [[elementary charge]] ''e'' is one of the fundamental [[physical constants]] and its accurate value is of great importance. In 1923, Millikan won the [[Nobel Prize]] in [[physics]] in part because of this experiment.
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| Aside from the measurement, the beauty of the oil drop experiment is that it is a simple, elegant hands-on demonstration that charge is actually quantized. [[Thomas Edison]], who had previously thought of charge as a continuous variable, became convinced after working with Millikan and Fletcher's apparatus.<ref name="Bandrawal2009">{{cite book|author=Praveen kumar Bandrawal|title=Nobel Awards Winner Physics|url=http://books.google.com/books?id=iWyQcso9rskC&pg=PT169|accessdate=14 December 2012|date=11 March 2009|publisher=Pinnacle Technology|isbn=978-1-61820-254-3|pages=169–}}</ref> This experiment has since been repeated by generations of physics students, although it is rather expensive and difficult to do properly.
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| In the last two decades, several computer-automated experiments have been conducted to search for isolated fractionally charged particles. So far (2007), no evidence for fractional charge particles was found over more than 100 million drops measured.<ref>[http://www.slac.stanford.edu/exp/mps/FCS/FCS_rslt.htm SLAC - Fractional Charge Search - Results<!-- Bot generated title -->]</ref>
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| ==Experimental procedure==
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| === Apparatus===
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| {{Refimprove section|date=December 2010}}
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| [[Image:Simplified scheme of Millikan’s oil-drop experiment.svg|right|thumb|upright=1.25|Simplified scheme of Millikan’s oil drop experiment]]
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| [[Image:Millikan’s oil-drop apparatus 1.jpg|right|thumb|upright=1.25|Oil drop experiment apparatus]]
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| Millikan’s and Fletcher's apparatus incorporated a parallel pair of horizontal metal plates. By applying a potential difference across the plates, a uniform electric field was created in the space between them. A ring of insulating material was used to hold the plates apart. Four holes were cut into the ring, three for illumination by a bright light, and another to allow viewing through a microscope.
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| A fine mist of oil droplets was sprayed into a chamber above the plates. The oil was of a type usually used in [[vacuum]] apparatus and was chosen because it had an extremely low [[vapour pressure]]. Ordinary oil would evaporate under the heat of the light source causing the mass of the oil drop to change over the course of the experiment. Some oil drops became electrically charged through friction with the nozzle as they were sprayed. Alternatively, charging could be brought about by including an ionising radiation source (such as an [[X-ray tube]]). The droplets entered the space between the plates and, because they were charged, it could be made to rise and fall by changing the voltage across the plates.
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| ===Method===
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| {{Refimprove section|date=December 2010}}
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| [[Image:Scheme of Millikan’s oil-drop apparatus.jpg|thumb|upright=1.25]]
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| Initially the oil drops are allowed to fall between the plates with the electric field turned off. They very quickly reach a [[terminal velocity]] because of friction with the air in the chamber. The field is then turned on and, if it is large enough, some of the drops (the charged ones) will start to rise. (This is because the upwards electric force ''F''<sub>E</sub> is greater for them than the downwards gravitational force ''F''<sub>g</sub>, in the same way bits of paper can be picked by a charged rubber rod). A likely looking drop is selected and kept in the middle of the field of view by alternately switching off the voltage until all the other drops have fallen. The experiment is then continued with this one drop.
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| The drop is allowed to fall and its terminal velocity v<sub>1</sub> in the absence of an electric field is calculated. The [[drag (physics)|drag]] force acting on the drop can then be worked out using [[Stokes' law]]:
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| :<math>F_{d} = 6\pi r \eta v_1 \,</math>
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| where ''v<sub>1</sub>'' is the terminal velocity (i.e. velocity in the absence of an electric field) of the falling drop, ''η'' is the [[viscosity]] of the air, and ''r'' is the [[radius]] of the drop.
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| The weight '''''w''''' is the volume ''D'' multiplied by the density ''ρ'' and the acceleration due to gravity '''''g'''''. However, what is needed is the apparent weight. The apparent weight in air is the true weight minus the [[upthrust]] (which equals the weight of air displaced by the oil drop). For a perfectly spherical droplet the apparent weight can be written as:
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| :<math>\boldsymbol{w}=\frac{4\pi}{3}r^3(\rho-\rho_{air})\boldsymbol{g}</math>
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| At terminal velocity the oil drop is not [[acceleration|accelerating]]. Therefore the total force acting on it must be zero and the two forces ''F'' and ''w'' must cancel one another out (that is, ''F'' = ''w''). This implies
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| :<math>r^2 = \frac{9 \eta v_1}{2 g (\rho - \rho _{air})}. \,</math>
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| Once ''r'' is calculated, ''w'' can easily be worked out.
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| Now the field is turned back on, and the electric force on the drop is
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| :<math>F_E = q E \,</math>
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| where ''q'' is the charge on the oil drop and ''E'' is the electric field between the plates. For parallel plates
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| :<math>E = \frac{V}{d} \,</math>
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| where ''V'' is the potential difference and ''d'' is the distance between the plates.
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| One conceivable way to work out ''q'' would be to adjust ''V'' until the oil drop remained steady. Then we could equate ''F''<sub>''E''</sub> with ''w''. Also, determining ''F''<sub>''E''</sub> proves difficult because the mass of the oil drop is difficult to determine without reverting to the use of Stokes' Law. A more practical approach is to turn ''V'' up slightly so that the oil drop rises with a new terminal velocity ''v''<sub>2</sub>. Then
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| :<math>q\boldsymbol{E}-\boldsymbol{w}=6\pi\eta\boldsymbol{(r\cdot v _2)}=\left|\boldsymbol{\frac{v_2}{v_1}}\right|\boldsymbol{w}</math>.
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| ==Fraud allegations==
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| There is some controversy raised by the historian [[Gerald Holton]] over the use of selectivity in the results of Millikan's second experiment measuring the electron charge. Holton (1978) pointed out that Millikan disregarded the data from a large set of the oil drops in his experiments without apparent reason. [[Allan Franklin]], a former high energy [[experimentalist]] and current [[philosopher]] of science at the [[University of Colorado at Boulder|University of Colorado]] has tried to rebut this point by Holton.<ref>{{cite journal|last=Franklin |first=A. |title=Millikan's Oil-Drop Experiments |journal=[[The Chemical Educator]]|volume=2 |issue=1 |year=1997 |pages=1–14 |doi=10.1007/s00897970102a}}</ref> Franklin contends that Millikan's exclusions of data did not affect his final value of ''e'' but concedes that there was substantial "[[cosmetic surgery]]" that Millikan performed which had the effect of reducing the [[Errors and residuals in statistics|statistical error]] on ''e''. This enabled Millikan to claim that he had calculated ''e'' to better than one half of one percent; in fact, if Millikan had included all of the data he threw out, it would have been to within 2%. While this would still have resulted in Millikan having measured ''e'' better than anyone else at the time, the slightly larger uncertainty might have allowed more disagreement with his results within the physics community. David Goodstein counters that Millikan plainly states that he only included drops which had undergone a "complete series of observations" and excluded no drops from this group.<ref>{{Cite journal | last = Goodstein | first = D. | authorlink = David Goodstein | title = In defense of Robert Andrews Millikan | journal = Engineering and Science |volume=63 | issue = 4 | pages = 30–38 | publisher = Caltech Office of Public Relations | location = Pasadena, Californi | year = 2000}}</ref>
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| ==Millikan's experiment as an example of psychological effects in scientific methodology==
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| In a commencement address given at the [[California Institute of Technology|California Institute of Technology (Caltech)]] in 1974 (and reprinted in ''[[Surely You're Joking, Mr. Feynman!]]''), physicist [[Richard Feynman]] noted:
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| <blockquote>
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| We have learned a lot from experience about how to handle some of the ways we fool ourselves. One example: Millikan measured the charge on an electron by an experiment with falling oil drops, and got an answer which we now know not to be quite right. It's a little bit off because he had the incorrect value for the viscosity of air. It's interesting to look at the history of measurements of the charge of an electron, after Millikan. If you plot them as a function of time, you find that one is a little bit bigger than Millikan's, and the next one's a little bit bigger than that, and the next one's a little bit bigger than that, until finally they settle down to a number which is higher.
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| </blockquote> | |
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| <blockquote> | |
| Why didn't they discover the new number was higher right away? It's a thing that scientists are ashamed of—this history—because it's apparent that people did things like this: When they got a number that was too high above Millikan's, they thought something must be wrong—and they would look for and find a reason why something might be wrong. When they got a number close to Millikan's value they didn't look so hard. And so they eliminated the numbers that were too far off, and did other things like that...<ref>[http://www.lhup.edu/~DSIMANEK/cargocul.htm Feynman, Richard, "Cargo Cult Science"] (adapted from 1974 [http://www.caltech.edu/ California Institute of Technology] commencement address), ''[http://www.lhup.edu/~DSIMANEK/home.htm Donald Simanek's Pages]'', [http://www.lhup.edu/ Lock Haven University], rev. August 2008.</ref><ref name="FeynmanLeighton1997">{{cite book|last1=Feynman|first1=Richard Phillips|last2=Leighton|first2=Ralph|last3=Hutchings|first3=Edward|title="Surely you're joking, Mr. Feynman!": adventures of a curious character|url=http://books.google.com/books?id=7papZR4oVssC&pg=PA342|accessdate=10 July 2010|date=1997-04-01|publisher=W. W. Norton & Company|location=New York|isbn=978-0-393-31604-9|page=342}}</ref>
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| </blockquote>
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| {{As of|2013}}, the accepted value for the elementary charge is {{val|1.602176565|(35)|e=-19|u=C}},<ref>[http://physics.nist.gov/cgi-bin/cuu/Value?e NIST Reference on Constants, Units and Uncertainty]</ref> where the 35 indicates the uncertainty of the last two decimal places. In his Nobel lecture, Millikan gave his measurement as {{val|4.774|(5)|e=-10|u=[[statcoulomb|statC]]}},<ref>{{cite speech | title = The electron and the light-quant from the experimental point of view | first = Robert A. | last = Millikan | authorlink = Robert Millikan | date = May 23, 1924 | location = Stockholm | url = http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-lecture.html | accessdate = 2006-11-12}}</ref> which equals {{val|1.5924|(17)|e=-19|u=C}}. The difference is less than one percent, but it is more than five times greater than Millikan's [[standard error]], so the disagreement is significant.
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| == References ==
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| {{Reflist}}
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| ==Further reading==
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| {{refbegin}}
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| * {{Cite book | author=Serway, Raymond A.; Faughn, Jerry S. | title=Holt: Physics | publisher=Holt, Rinehart and Winston | year=2006 | isbn=0-03-073548-3}}
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| * {{Cite book | author=Thornton, Stephen T.; Rex, Andrew | title=Modern Physics for Scientists and Engineers (3rd ed.) | publisher=Brooks/Cole | year=2006 | isbn=0-495-12514-8}}
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| * {{Cite book | author=Serway, Raymond A.; Jewett, John W. | title=Physics for Scientists and Engineers (6th ed.) | publisher=Brooks/Cole | year=2004 | isbn=0-534-40842-7}}
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| {{refend}}
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| ==External links==
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| {{commons category|Oil-drop experiment}}
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| * Thomsen, Marshall, "''[http://www.physics.emich.edu/mthomsen/sege.htm Good to the Last Drop]''". Millikan Stories as "Canned" Pedagogy. Eastern Michigan University.
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| * CSR/TSGC Team, "''[http://www.tsgc.utexas.edu/floatn/1997/teams/UT-austin.html Quark search experiment]''". The University of Texas at Austin.
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| * The oil drop experiment appears in a list of [http://physics.nad.ru/Physics/English/top10.htm Science's 10 Most Beautiful Experiments] originally published in the [[New York Times]].
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| * Engeness, T.E., "''[http://people.ccmr.cornell.edu/~muchomas/8.04/Lecs/lec_Millikan/Mill.html The Millikan Oil Drop Experiment]''". 25 April 2005.
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| *{{Cite journal | author=Millikan R. A. | title=On the elementary electrical charge and the Avogadro constant | journal=Physical Review | series = Series II | year=1913 | volume=2 | pages=109–143 | url=http://www.aip.org/history/gap/PDF/millikan.pdf |bibcode = 1913PhRv....2..109M |doi = 10.1103/PhysRev.2.109 }}, Paper by Millikan discussing modifications to his original experiment to improve its accuracy.
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| * Hudspeth, P. and Klingler, R., [http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.1302567 A search for free quarks in the micro gravity environment of the International Space Station ], ''AIP Conf. Proc.'' 504, 715 (2000). A variation of this experiment has been suggested for the [[International Space Station]].
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| * Perry, M. F., "[http://faculty.mint.ua.edu/~pleclair/PH255/papers/Millikan/phys_today_millikan.pdf Remembering the oil-drop experiment]", ''Physics Today'', May 2007, 56-60.
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| {{DEFAULTSORT:Oil Drop Experiment}}
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| [[Category:Physics experiments]]
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| [[Category:Electrostatics]]
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| [[Category:Foundational quantum physics]]
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| [[Category:1909 in science]]
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