* https://phet.colorado.edu/sims/html/balloons-and-static-electricity/latest/balloons-and-static-electricity_all.html
* https://javalab.org/en/conductor_and_insulator_en/
* https://www.physicsclassroom.com/Physics-Interactives/Static-Electricity/Charging/Charging-Interactive
https://phet.colorado.edu/sims/html/charges-and-fields/latest/charges-and-fields_en.html
Campo eléctrico generado por un cascarón esférico cargado uniformemente