Two pieces of optically flat glass (n = 1.50) touch at one edge and a separated by a thin stretched fiber at the opposite edge. Light of wavelength 500 nm is shone from above and 100 dark fringes are counted. How thick is the fiber?
a. 25 um (micro)
b. 13 um
c. 5 um
d. 100 um
e. 50 um