Electroscope question

[username]

Ok, this is not really homework so maybe it needs to be moved some where else.

Made a basic electroscope out of a wine bottle a while ago, charged up a ballon brought it close to the end of the scope and the leaves seperated as expected, but when I quickly moved the ballon away from the scope the leaves separated 5 times wider for a few seconds then fell back. Why is this, is it due to some sort of sudden charge backwash in the process of depolarisation (is that a term :/) ?

Thx

[Chi Meson]

Not a "backwash" definitely. I think the following is correct:

the leaves were together before the balloon appraoached. The balloon came close and the leaves separated...

at this point, did the leaves come close to, or touch the sides of the bottle?

If they did, then they deposited a charge on the inside surface which then repelled the leaves slightly. THis would "squeeze" the leaves between opposing forces on both sides. When the balloon is taken away, the leaves desire to take back the charges that were deposited on the sides of the bottle (opposites attract, so all separated charges attract). The leaves come close to, or touch, the sides and pick up the charges and now its neutral again.

[username]

Voila, thank's that one has been bugging me for ages.

EDIT: I guess if I did not remove the ballon quickly away the charge on the inside of the bottle would then have time to dissipate reducing the effect.