Understanding Cylindrical Capacitors: Charged vs. Disconnected

[Toby_phys]

Homework Statement

Normally this style of question wouldn't be too bad, however the 2 different parts confused me. Surely once set to a potential V, it would stay at that potential - it doesn't need to stay connected

How are the 2 parts any different from each other?

 

[gneill]

Withdrawing the inner cylinder changes the capacitance. If the charge is fixed (no external connection), how does potential difference vary when capacitance varies?

Note that this is similar to the problem where a parallel plate capacitor has its plate separation varied while either connected to, or not connected to, a voltage source.

 

[Toby_phys]

ahh, so its charged up, disconnected and then withdrawn? I guess if it were withdrawn before being charges it would be the same as a smaller capacitor