I'm curious about electron trapping by electrostatic force. A simple scenario can be ... A perforated, conductive, hollow sphere in a vacuum, connected to a negative high voltage source. I want to calculate how much electrons it can hold (total charge of it). The relation between sphere voltage, radius, total charge. Sphere is perforated because i do not want to hold the electrons 'physically' like a gas although i don't think that is possible for conductive things. Simple coulomb's law should be enough but I don't know how to consider individual electrons repealing each other. PLEASE HELP ME. Thanks.