I am sorry for the late reply. I hope the following simulation is what you need.
You can drag the arrow to change initial velocity.

/htdocs/ntnujava/ejsuser/2/users/ntnu/fkh/chargedParticleTowoPlates_pkg/chargedParticleTowoPlates.propertiesFull screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
Download EJS jar file(1200.4kB):double click downloaded file to run it. (19 times by 16 users) , Download EJS source View EJS source