1. The problem statement, all variables and given/known data Two optically flat plates of glass are separated at one end by a wire of diameter 0.250 mm; at the other end they touch. Thus, the air gap between the plates has a thickness ranging from 0 to 0.250 mm. The plates are 15.0 cm long and are illuminated from above with light of wavelength 550.0 nm. How many bright fringes are seen in the reflected light? 2. Relevant equations t=m(lambda) 3. The attempt at a solution I know that there is two phase changes, so with this apparatus, there has to be a (1/2) added to create constructive interference. I also know that the ray has to travel through the thickness once, and then again, so the distance would be 2t. I tried solving for t via the equation 2t=(m+1/2)(lambda) and solving for t. That gives me the distance, but I'm not sure what to do from there. Am I on the right track?