How about the following one! Let me know what need to be changed!

It is my habit to create simulation for teaching and learning. Let me know whatever you have in mind and I will try to find free time to do it.
:-)

/htdocs/ntnujava/ejsuser/2/users/ntnu/fkh/FermatPrinciple2_pkg/FermatPrinciple2.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(976.8kB):double click downloaded file to run it. (8 times by 5 users) , Download EJS source View EJS source