A Thin Uniform Film of Oil That Can Be Varied

Multiple Choice

A thin uniform film of oil that can be varied in thickness covers a sheet of glass of refractive index 1.52.The refractive index of the oil is 1.64.Light of wavelength 555 nm is shone from air at normal incidence on the film.Starting with no oil on the glass,you gradually increase the thickness of the oil film until the first interference maximum in the reflected light occurs.What is the thickness of the oil film at that instant?

A) 139 nm
B) 169 nm
C) 183 nm
D) 84.6 nm
E) 91.3 nm