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.
VIEW or DOWNLOAD ejs xml source
then click to translate strings for selected locale.

Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop.