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I am reading the volume 2 of the Feynman's Lectures on Physics, and something is bothering me when he calculates the dipole moment of a single atom induced by an extern field :

https://books.google.co.uk/books?id...=onepage&q=feynman dipole single atom&f=false

Indeed, he states that : "p = q"_{e}x

But why ? I would use in general : "p = Zq" where Z is the number of electrons in the atom._{e}x

xis the displacement of the center of charges of the electrons, and thusxis also the displacement of each electron.

Could you explain his reasoning ? It is not the first time he uses a single electron charge instead of Z in his calculations, and I do not understand.

Thanks.

PS : Andqis obviously equal to the charge of one electron and note equal to Z*(charge), because he uses then e² = q²_{e}_{e}/4piε_{0}(we can also see it in the mechanical equation of motion).

Moreover, when he the does his calculations for the Helium atom, he keeps using q_{e}= charge ofoneelectron and does not use a new value for Z. And that is exactly what I find weird: he gets the good results event without having taken Z = 2.

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# Feynman -- Atomic dipole

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