Electric potential problem ?

[ngkamsengpeter]

I want to know that why electric potential of the electroscope which is charge positive decrease when a rod which is earthed is brought near to the electroscope .

 

[andrevdh]

Well an intuitive explanation for this is that the positive charge on the electroscope will induce a negative charge on the rod, that is it draws some electrons onto the tip of the rod closest to the electroscope. The presence of this negative charge on the rod will repel electrons from the disc at the top of the electroscope downwards towards the leaves of the electroscope thereby causing them to collapse a bit.

 

[ngkamsengpeter]

Well an intuitive explanation for this is that the positive charge on the electroscope will induce a negative charge on the rod, that is it draws some electrons onto the tip of the rod closest to the electroscope. The presence of this negative charge on the rod will repel electrons from the disc at the top of the electroscope downwards towards the leaves of the electroscope thereby causing them to collapse a bit.

But I mentioned that the electroscope is charged positive so there should be no electron on the electroscope right ?

 

[andrevdh]

Only a slight charge imbalance (different amounts of positive and negative) is created in a body when it is charged up, in this case only a fraction of the electrons on the surface of the conducting part of the electroscope is removed. This involves some of the "outer" conduction electrons of the atoms. There will still be plenty of electrons left in the material. It takes quite a lot of energy to strip the inner electrons off the atoms. So the conduction electrons will be removed gradualy as it is charged up. Long before the inner ones are ripped out of the atoms all sorts of phenomena will start to manifest like sparks, discharges in the air and glowing light around the charged object.