After 3 minutes, where does the charge on the capacitor go?
Key Points: capacitor leak through internal leaks (dielectrics)
We see that the voltage has decayed. It is likely that the charge has leaked through the dielectric in the capacitor from one plate to the other.
Is there a significant difference while the electrometer is connected?
Key Points: Leak through measurement devices (voltage probes)
The electrometer offers another path for charge to leak from one plate to the other.
However, it has such a high internal resistance (about 1014 ohms) that we don't see a large effect on the rate at which the charge leaks.
Is there a difference with the vernier probes?
The capacitor is discharging while the voltmeter is connected. This is because the voltmeter provides a path for charge to leak from one plate to the other. The voltmeter has a much lower internal resistance than the electrometer and so we see that it allows a noticeable leak in the capacitor. We see that the capacitor does not leak as much while it is disconnected.