http://home.phy.ntnu.edu.tw/~lookang/Physletbuilder/Efieldgeneratedbyonepositiveandonenegativecharge.html

PS:
i have to delete this applet here, cos only can display one :)


Please check out  [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=539.0]Electric field structure and Field lines for two point charges +/-[/url] for similar applet created with EJS.