Imagine that an incident light wave encounters a thin film. Some of that light wave will be reflected off of the top surface of the thin film (call this Wave 1), while the rest will be transmitted through the film. Some of this transmitted light (Wave 2) will reflect off the back surface of the film and move back through the thin film and out into the original medium of the incident light wave. If the thin film has a thickness t, then what is the path length difference between Wave 1 and Wave 2?

a) t/4
b) t/2
c) t
d) 2t