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The electric field in a metal is zero in electrostatics. But in Rutherford gold foil experiment, alpha particles get deflected from the gold foil showing presence of electric field there. I discussed the question outside the forum and found the following answers which don't seem correct to me:

(a) Gold is not a metal but is a semi metal

(b) When alpha particle moves in gold, this is not an electrostatic situation.

(c) The moving alpha particle creates a magnetic field which shifts the electron clouds to create the electric field.

(d) The electric field inside a metal is zero only in an average sense.

(e) The alpha particles are deflected from the surface of the gold foil and electric field may exist at the surface of a metal.

What could be the possible explanation?

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I vote for the list (d) The electric field inside a metal is zero only in an average sense.

The zero electric field inside a conductor is a concept of classical electro-magnetism. Its formulations are valid only in the area of macroscopic theory. The typical length scale is micro-meter. In Jackson's book, a example of obtaining the macroscopic quantity averaged over microscopic quantities was show in chapter 6.

For Rutherford's back scattering experiment, it is a microscopic theory. The electric field experienced by an $\alpha$ particle is in an atomic scale. Where an $\alpha$ meets a $Au$ atom, they are approached each other in distance of nano-meter.

Th electric field $\vec E(\vec r)$ is obtained by averaging over millions of the $Au$ atoms, a volume of scale micro-meter around the position $\vec r$. The average is over millions of $Au$ atoms.

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