The last chapter was concerned with the phenomenology of magnetic fields, without any thought of the atomic processes involved. Believing, as we do, that electric currents are due to the motion of charged particles, we naturally enquire what magnetic field is produced by a single moving particle, and what forces it experiences when it moves in a magnetic field. To take the second question first, let us postulate a simple model of the current in a wire, imagining it to result from the motion of n charged particles per unit length of wire, each carrying charge e and each moving with the same velocity v. Then in unit time the particles contained in a length v pass a given point, so that i = nev. The force on a length dl of wire when a field B is applied is i dl ˄ B, which may be written as (n dl)ev ˄ B as if each of the n dl particles experienced a force ev ˄ B and, being unable to escape from the wire, transmitted this force to the lattice structure of the metal by collisions either within the wire or at the boundary.
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- Electron Optics: V. E. Cosslett, Electron Optics, Oxford U.P.Google Scholar
- Cyclotron: E. Segré, Nuclei and Particles, Benjamin.Google Scholar
- Electrons in Metals: J. M. Ziman, Electrons in Metals, Taylor and Francis.Google Scholar
- Plasmas: L. Spitzer, Physics of Fully Ionized Gases, Interscience.Google Scholar
- Van Allen Belts: S. F. Singer and A. M. Lenchek, ‘Geomagnetically Trapped Radiation’, in Progress in Elementary Particle and Cosmic-ray Physics, Vol. 6, North-Holland.Google Scholar