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Are the ions in a fluorescent lamps concentrated near the electrodes , and just the electrons move to the other electrode or the positive mercury ions move too?

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The speed of the ions is slower than that of the electrons by a factor of the ratio of masses (to first order) which is of order 40,000, and in a alternating field they don't go far enough to bother ourselves about before the field reverses.

So, in principle yes, they drift, but they don't move far enough to accumulate near the cathode and for practical purposes you can ignore it.

More over, if you did get a large separation it would surpress the field.

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So at any given moment , will there be positive ions in the tube ? if yes, is this number constant, depending on the volume , voltage or whatever? –  Abdelrahman Esmat Jan 19 '13 at 16:46

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