Abstract
The study of the passage of electricity through gases had lagged behind the corresponding study on metals and liquids. Faraday himself had engaged in research on electrical discharges in gases as early as 1838 but was hampered by the inefficiency of his vacuum pumps.
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Notes
- 1.
We note that this discovery was instrumental in the later mass-production of incandescent bulbs by Thomas Edison.
- 2.
Lenard contributed significantly to the development of this field. For this, and his work relating to the photoelectric effect (see Sect. 13.1.2) Lenard was awarded the 1905 Nobel Prize for Physics.
- 3.
Arnold Sommerfeld was born in 1868 in Königsberg (East Prussia), the son of a physician. He studied mathematics at the university of his hometown graduating in 1891. After military service he worked at the mathematical institute of the University of Göttingen, where he delivered a paper on the mathematical theory of the diffraction of light. In 1897 he became a professor of mathematics at the Mining Academy of Clausthal, and in 1900 a professor of mechanics at the Technical Unversity of Aachen. In 1906 he was appointed to the chair of theoretical physics at the University of Munich, and occupied this post until he was awarded emeritus status in 1938. He was an excellent researcher and an esteemed and popular lecturer. He inspired a number of students including Wolfgang Pauli, Werner Heisenberg, Peter Debye, Hans Bethe and others. Today he is remembered mostly for his extension of Bohr’s model of the atom (see Sect. 13.2.3) and his free-electron theory of metals (see Sect. 14.7.3). During his emeritus period he compiled his Lectures on Theoretical Physics, which were published in six volumes between 1943 and 1953. He died in 1951 following a traffic accident.
- 4.
The forces acting on an oil drop, falling in air between the horizontal plates of a capacitor, are: its weight, a drag force due to the viscosity of the air, an upthrust force (which equals the weight of the air displaced by the oil drop), and the force qE, where q denotes the total charge on the drop and E is the electric field (in the vertical direction) between the plates of the capacitor. All the forces except the latter could be determined with reasonable accuracy by measuring the radius of the oil drop and the density of the oil. By adjusting the value (E) of the electric field so as to obtain a terminal (constant) velocity of the drop (implying a net zero force), one determines the charge q on the droplet. In every case, q was found to be an integral multiple of a certain unit, which was taken as the charge (e) of the electron.
- 5.
S. Dushman gave the first quantum–mechanical derivation of Eq. (11.8), on the basis of Sommerfeld’s free-electron theory of metals. According to this theory, the pre-exponential constant in Eq. (11.8 ) is: A=emk2 /(2π 2 ћ 3) = 120 A/(cm2deg2), where e and m are the charge and mass of the electron, k is Boltzmann’s constant, and \( \hbar \)is Planck’s constant.
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Modinos, A. (2014). Cathode Rays and X-rays. In: From Aristotle to Schrödinger. Undergraduate Lecture Notes in Physics. Springer, Cham. https://doi.org/10.1007/978-3-319-00750-2_11
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