[n-gauge]

Here's another one - put an oscilloscope across a capacitor and turn off the circuit it's connected too. Quickly short the capacitor with something, and watch the voltage on the oscilloscope as the capacitor discharges, remove the short and watch it start recharging slightly.

Where does this charge come from?

[analog31]

It's a non ideal behavior of a cap, and some dielectric types have it worse than others. I once made a sample-and-hold for a data acquisition system, and must have tried every type of cap in the bin until I found one that resulted in the least amount of correlation between subsequent readings. I think it was a polypropylene type. Mica was the worst. I don't think I tested an electrolytic.

[Cyph0n]

1. The short is not an ideal short circuit because whatever you use will have some resistance.

2. The shorted capacitor will discharge some current into the short wire and some into the oscilloscope’s capacitor (probably wire capacitance).

3. Once you remove the short wire, some current will flow back into the capacitor under test to equalize the voltage.

[rathel]

Dielectric absorption.

[cushychicken]

Potentially the scope cable. Cables have capacitance too.

That, or this is the "memory effect" I've heard about in certain dielectrics acted out.

[edoceo]

It's in the cap