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The Kaufmann-Neumann experiment is a type of experiment in physics used to measure the dependence of the inertial mass of an object on its velocity. The historical importance of a series of this experiment performed by various physicists between 1901 and 1914 is due to the results being used to test the predictions of special relativity. Its developing precision and data analysis, and the resulting influence on theoretical physics, during those years is still a topic of active discussion, since the early experimental results at first contradicted Einstein's then newly published theory, but later versions of this experiment confirmed it.

Contents

[edit] History

[edit] Historical context

In 1896 Henri Becquerel had discovered the radioactive decay in a variety of chemical elements. Subsequently, the beta radiation from these decays was discovered to be the emission of a negatively charged particle. Later these particles were identified with the electron, discovered in cathode ray experiments by J.J. Thomson in 1897.

Walter Kaufmann began to experiment with these particles using a device similar to a cathode ray tube, where the source of the electrons was the decay of radium that was placed in a vacuated tube. Applying electric and magnetic fields to measure the charge and mass of the particles, he published a first analysis of his data in 1901.[1] (This was four years before Albert Einstein published his theory of special relativity.) At the time he found that the charge of the electrons did not change with the speed of the particle, however its inertial mass was changing. In his original analysis he separated the measured total mass into a mechanical (true) mass and an electromagnetic (apparent) mass. In series of updates and improved experimental techniques from 1902 to 1905[2][3][4], he then started to compare his results with theoretical predictions trying to explain the mass change.

[edit] Competing theories

In 1902, Max Abraham published a theory based on the assumption that the electron was a rigid, perfect sphere, with its charge being distributed evenly on its surface.[5] It was constructed with the concept of the aether assumed to be valid.

At about the same time Hendrik Lorentz applied his 1895 model, where moving objects are "deformed" when moving within the aether.[6] He predicted that electrons were spreading their charge throuhgout their volume and in Kaufmann's experiment their shape would be compressed in the direction of motion and stay unchanged in the transverse directions.

A similar theory was construced by Alfred Bucherer, with the difference that the total volume occupied by the deformed electron was assumed unchanged.[7] It turned out, that this theory's prediction were indistinguishable from Abraham's theory.

When after 1905 the theory of special relativity[8] was used to describe the measured data, it predicted the change of the point-like electron's mass due to the properties of the transformation between the rest-frame of the particle and the laboratory frame in which the measurements were performed.[9] Mathematically, this calculation predicts the same dependence between velocity and mass as Lorentz's theory, although it assumes very different physical concepts.

[edit] Evolution of experiments

From 1901 until 1914 multiple physicists performed this type of experiment and provided various data sets to compare the results with theory. Using similar techniques, but improving their setup and analysis steps, G. Neumann published the first data conclusively showing the validity of the Lorentz-Einstein formula[10] describing how inertial mass was affected by the speed of an object.

[edit] Confirmation of special relativity

[edit] Planck's evaluation

Shortly after Kaufmann published his results and the conclusions of his analysis (which ostensibly disproved the Lorentz-Einstein formula), Max Planck decided to re-analyze the data obtained by the experiment. In 1906 and 1907, Planck published[11][12] his own conclusion on the behavior of the inertial mass of electrons with high speeds.

Using just nine data points from Kaufmann's publication in 1905, he recalculated the exact setup of the fields for each point, and predicted the measurements using the two competing theories.

[edit] Bucherer's experimental improvements

[13]

[14]

[edit] Neumann experiment

[edit] General history of science

[edit] See also

[edit] References

[edit] Notes

  1. ^ W. Kaufmann, Die magnetische und die elektrische Abklenbarkeit der Becquerelstrahlen und die scheinbare Masse des Elektrons, Nachr. K. Ges. Wiss. Goettingen 2, p. 143 (1901)
  2. ^ W. Kaufmann, Nachr. K. Ges. Wiss. Goettingen 3, p, 291 (1902); Die elektromagnetische Masse des Elektrons, Phys. Zeitschr. 4, p. 54 (1902)
  3. ^ W. Kaufmann, Nachr. K. Ges. Wiss. Goettingen 4, p. 90 (1903)
  4. ^ W. Kaufmann, Über die Konstitution des Elektrons, Sitzungsber. K. Preuss. Akad. Wiss. 2, p. 949 (1905)
  5. ^ M. Abraham, Dynamik des Elektrons, Gött. Ges. Wiss. Nachr. 20, p. 41 (1902)
  6. ^ H.A. Lorentz, Electromagnetic Phenomena in a System Moving with any Velocity less than that of Light, Proc. Acad. Sci. Amsterdam, 6, p. 809 (1904)
  7. ^ A.H. Bucherer, Mathematische Einführung in die Elektronentheorie, Teubner, Leipzig 1904, p. 57
  8. ^ A. Einstein, Zur Elektrodynamik bewegter Körper, Ann. Phys. 17, p. 891–921 (1905)
  9. ^ C.E. Guye, C. Lavanchy, Vérification expérimentale de la formule de Lorentz-Einstein par les rayons cathodiques de grande vitesse, Compt. Rend. Acad. Sci. 161, p. 52 (1915)
  10. ^ G. Neumann, Die träge Masse schnell bewegter Elektronen, Ann. Phys. 45, p. 529 (1914)
  11. ^ M. Planck, Die Kaufmannschen Messungen der Ablenkbarkeit der beta-Strahlen in ihrer Bedeutung für die Dynamik der Elektronen, Verhandlungen der Deutschen Physikalischen Gesellschaft, 8 (1906)
  12. ^ M. Planck, Nachtrag zu der Besprechung der Kaufmannschen Ablenkungsmessungen, Verhandlungen der Deutschen Physikalischen Gesellschaft, 9 (1907)
  13. ^ A.H. Bucherer, Phys. Zeitschr. 9 (1908), p. 755; Ber. d. deutschen Phys. Ges. 6 (1908), p. 688
  14. ^ A. Bucherer, Die experimentelle Bestätigung des Relativitätsprinzips, Annalen der Physik, 28 (1909)

[edit] External links