Capacitance of a capacitor in which the first plate is (-)vely charged

1. May 12, 2013

shiv_99

I have read that if we have an isolated positively charged conductor, we can increase its self capacitance by bringing an identical conductor close to it and then earthing it, so, that the second conductor develops a negative charge and thereby helps in reducing the net electric potential on the surface of the first conductor. (and so capacitance of conductor will increase as V will decrease).

BUT my question is
a)what happens to the self capacitance of the second conductor (does it become infinite? if so then why does the capacitance of the capacitor as a whole does not equal infinity!)

b)if the first conductor is negatively charged and another identical conductor is brought close to it, won't the self-capacitance of the first conductor decrease.

2. May 14, 2013

sophiecentaur

Where did you read that? I think this is only a question of definitions.
Self capacitance describes the ratio of charge to absolute potential for an isolated object. If you introduce a nearby earthed conductor, then you would not only be seeing 'self' capacitance but the mutual capacitance of the two objects.
The "self capacitance of the second conductor" would be the same as the self capacitance of the Earth, to which it's connected. This is about 700µF, iirc.