1. Select positive/negative charge and click inside the simulation area to add particles at that point. (Added particles can be fixed position or freely moving particles). You can add rectangle wall (provide x,y as top-left corner and width/height (w/h) values) or circular wall (provide x,y as center and R as radius) Change Ex or Ey if you need uniform electric field.

Virtual Physics laboratory Original URL

Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.