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## Main Question or Discussion Point

Hello,

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=uaQfAQAAQBAJ&pg=SA11-PA2&lpg=SA11-PA2&dq=feynman+dipole+single+atom&source=bl&ots=6nmZCqHDMk&sig=cd6wOGCKh9E9227ZX-a8KKhTqlM&hl=fr&sa=X&ei=NuI8VbHdI8v9UOSvgOAD&ved=0CDEQ6AEwAQ#v=onepage&q=feynman dipole single atom&f=false

Indeed, he states that : "

But why ? I would use in general : "

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 : First, I thought that was because the square of the natural pulsation ω

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=uaQfAQAAQBAJ&pg=SA11-PA2&lpg=SA11-PA2&dq=feynman+dipole+single+atom&source=bl&ots=6nmZCqHDMk&sig=cd6wOGCKh9E9227ZX-a8KKhTqlM&hl=fr&sa=X&ei=NuI8VbHdI8v9UOSvgOAD&ved=0CDEQ6AEwAQ#v=onepage&q=feynman dipole single atom&f=false

Indeed, he states that : "

**p = q**"_{e}xBut why ? I would use in general : "

**p = Zq**" where Z is the number of electrons in the atom._{e}x**x**is the displacement of the center of charges of the electrons, and thus**x**is 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 : First, I thought that was because the square of the natural pulsation ω

_{0}depended on Z, which means that ω²_{0}(Z) = Zω²_{0}(Z=1), which would simplify the Z replacing ω²_{0}(Z) by Zω²_{0}(Z=1) ; but Feynman seems to use ω_{0}= ω_{0}(Z) and not ω_{0}(Z=1) everywhere, so it does not matter.