Lets say we have an evacuated glass tube. In that glass tube we have a gas of some atom say .... ooo... mercury. (i wonder this could be goin ) Also in that glass tube we have 2 plates at the end, one is a cathode and one is a coleting palte held only slightly negative while in between the two plates is a postiive grid. My question is : the gas which fills the tube - will it remain betwee nthe cathode and the postiive grid? Why? Is it because despite the netrality of the atom, the atom will not be stable if it was located anywhere else in the tube 9because of induced dipoles)? Then the atom will locate itself to a location where the net electric field iis zero?