optics_p01.shtml
optics_p02.shtml
optics_p03.shtml


prb1.html (source and mirror - find focal length)
prb5.html (index of refraction - change values)
prb11.html (two lenses - find focal length of each)
prb12.html (two lenses in tandem .. one stronger than other)
prb13.html (hidden lenses .. two of them .. put weak diverging?)
prb15.html (hidden object - red line instead of lens .. what is it?)