1© I.H.Hutchinson 1999-2011
2[Feynman 21-6]
3The potential can always be altered by adding a constant, without changing E. This freedom can be considered equivalent to choosing the origin at which ϕ = 0.
4satisfying |B| → 0 as |x| → = ∞ fast enough
5[Feynman 21-6]
6An alternative definition can be invoked, equivalent to this first definition but in the frame of reference in which the single particle (1) is stationary and the particles of density n2 are moving.
7It also shows the fundamental incoherence of the notion of the total number of collisions per unit length and concepts that depend on it such as the average change in some parameter per collision, which some authors unfortunately employ.
8The factor of 2 here is our only real artifice. It gives the argument of the logarithm equal to that obtained by a full quantum calculation
9This proportionality can be traced to the inverse dependence of the energy transfer in a collision on m2, but only because cancellation of reduced mass factors occurs in the product Q b902.
10See M.Born "Atomic Physics" 8th ed., Blackie p199, for a derivation of the Thomas-Fermi distribution of electron density around an atom based on the Pauli exclusion principle and a continuum approximation.

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