thanks to lim yi xian

I told my classes Loo Kang edited the lens applet and what the lens applet was capable of doing, and the girls went "WAHHHH......"... Haha.. Thanks Loo Kang!
A little touchup to the applet if you got time LK:
for divergent lens light ray, the arrow should be dotted and pointing in opposite direction? See attached. Thanks again!

[b][color=blue]dotted lines is difficult (not available) in EJS, will not implement
opposite direction done thanks to [/color][/b]