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In electrostatics, we usually consider charge to be continuous on any body, to calculate the electric field of the body. For eg. I had proved the Shell Theorem taking an infinitesimal charge of $dq$ on the sphere. But we also know that charges are quantized (In terms of electrons and protons). They are finite and not infinitesimal. So is considering them continuous an approximation or is there a reason to why we can do it?