How Does Thickness Affect Phase Change in Thin Film Interference?

[Dr3w529]

I basically understand the idea of the changes in phases of interference in thin films but i was hoping for a better explanation. i understand that the thickness of the lens effects the the exit phase but i don't know why PLEASE HELP! Thank you

 

[Hootenanny]

A good tutorial is given here;

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/interf.html#c1

~H