If one plate of an isolated charged parallel plate capacitor is earthed, then that plate must have a potential zero after being earthed as that is what earthing an isolated conductor does, but potential on each plate is only due to the charges on the other plate. Since the other plate(the one which is not earthed) is isolated and non-neutral, potential due to it on the earthed plate should not change. As surface charge density on the unearthed plate cannot be zero... how on earth will I manage to get the potential of the earthed plate to be zero without changing the charge on the other plate?
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asked Jul 13, 2023 at 16:05
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2 Answers
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It depends how you charged your capacitor. a) You first earthed bot plates and then carged one for example with +Q then one side of your C has -Q on the inside, +Q on the outside, if you connect it to earth the +Q outside go to earth ( or -Q from earth comes to the outside) If you connect bot sides in the Beginning to a high potential both plates max have the same positive charge say Q . Charging one side then with additional 1Q gives you for example +2Q on one side, +1Q on the inside of the other , so the same potential difference. Now connecting one side to earth both stay the same. So what happens is different from the initial potential to earth.
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how on earth will I manage to get the potential of the earthed plate to be zero without changing the charge on the other plate?
Earthing (grounding) one plate causes the potential (voltage) of the other plate to be measured with respect to earth (ground). It does not effect the charge on the capacitor. Think of using a voltmeter with the negative lead connected to earth (ground) and the positive lead connected to the ungrounded plate of the capacitor.
answered Jul 13, 2023 at 17:53