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Image from the March paper discussed below. A couple of weeks ago, io9 ran a piece about the old accusations that Robert Millikan manipulated his data for the electron charge with the headline Did a Case of Scientific Misconduct Win the Nobel Prize for Physics?
Hertz was creating and detecting waves using spark gaps— discharging a current through a small gap to make a spark in the air produced a blast of radiation, which he then detected by its ability to trigger a spark between another pair of electrodes some distance away.
He noticed that he got bigger sparks when there was a clear path for the light from the first spark to travel to the second spark gap. This was a result of photoelectric emission: This seems like it ought to be easy to explain, but classical physics turned out not to do a very good job of it, as I explained back in the pre-ScienceBlogs days of this blog.
This led to the two papers above, and contributed to Nobel Prizes for both Einstein the photoelectric effect is the only specific theory mentioned in his prize citation and Millikan. The January paper features maybe the greatest passive-aggressive introduction in the history of science: I have in recent years been subjecting this experiment to some searching experimental tests from a variety of viewpoints, and have been led to the conclusion that, whatever its origin, it actually represents very accurately the behavior… of all the substances with which I have worked.
But whatever his opinion, Millikan was above all else dedicated to getting experimental physics right, and in that paper, he clears up a lot of the confusion surrounding the previous attempts to test the theory. This involves a lot of extremely fussy experimental work— he performed all his experiments in very high vacuum, including forming the metal surfaces under vacuum, thus eliminating the effects of surface contamination.
The stray light issue in particular makes an enormous difference in the results.
Having established that the model worked, Millikan then put it to use, in the March paper. He works with everything under vacuum, blocks out stray light, tests the effects of contact potentials, and investigates second-order sources of error like reflected light and possible photoemission from the metal cylinder used to screen out external electric fields.
In the conclusion of the March paper, he opens by saying: Perhaps it is still too early to assert with absolute confidence the general and exact validity of the Einstein equation.
Nevertheless, it must be admitted that the present experiments constitute very much better justification for such an assertion than has heretofore been found, and if that equation be of general validity, then it must certainly be regarded as one of the most fundamental and far reaching of the equations of physics… and in the very next sentence he writes: Yet the semi-corpuscular theory by which Einstein arrived at his equation seems at present to be wholly untenable.
Now, there are still some issues with Millikan from a modern perspective. His is the only name on these papers, as was the style in those days, but he clearly had help from a couple of students, A.
Kadisch, and he thanks Walter Whitney for doing spectroscopy to determine the wavelengths of light from his source. By modern standards, those people would probably be co-authors. But then, he also wrote: To construct tubes in which these operations can all be performed in rapid succession, particularly when the substances to be studied are, as in this case, the inflammable alkali metals, sodium, potassium and lithium, is not at all easy, and such success as is being obtained in these experiments is due in no small degree to the skill and experience of the mechanician, Mr.
Julius Pearson, who has from the start made all the tubes and contributed not a little toward their design. Would this have been worth a Nobel by itself, without the disputed electron charge experiments?
It is an extremely important and unjustly overlooked bit of work, though, which cleared up some controversies about earlier measurements, and played an important role in locking up the case for quantum theory. Now you know, as they say, the rest of the story.Let us consider a glass tube (discharging tube) which consists of two electrodes; anode(A) an cathode(c).
It is connected as shown in fig. The experimental setup shows the Millikan’[s experiment to determine the value of plank’s constant as well as to verify the Einstein’s photoelectric effect.
Dec 17, · Einstein’s theory of photoelectric effect. Photoelectric effect: The process in which visible light, x rays, or gamma rays incident on matter cause an electron to be ejected. The ejected electron is called a photoelectron. Building a quantum computer can sometimes yield unexpected benefits — like providing the right environment to demonstrate that Albert Einstein's theory of special relativity is, in fact, correct.
This led to the two papers above, and contributed to Nobel Prizes for both Einstein (the photoelectric effect is the only specific theory mentioned in his prize citation) and Millikan. Foremost among them was the photoelectric effect: the ejection of electrons from a metal when irradiated by light.
The wave theory of light could not yield a satisfactory account of this, since the energy of a wave is spread over its entire surface. Focus: Centennial Focus: Millikan’s Measurement of Planck’s Constant.
April 22, • (the photoelectric effect), So Millikan’s paper is not at all, as we would now expect, an experimental proof of the quantum theory of light.