I've found a problem about 2 identic capacitors which have the same voltage. One of them is sinked in oil and after that the 2 capacitors are connected in series. The problem ask for the for the energy variation. I've done the problem but I don't understand something: When the capacitors are conected they must change charge between them because of the voltage difference. They alredy had the same charges and I know that two capacitors connected in series will have the same charge. So how is possible to change charge between them?