In a certain  region A to in B  thin  film, we get 10 fringes with light of wavelength 4358  ÅThe number of fringes observed in the same region with wavelength 5893 Åwill bi

Let n1, and n, be the number of fringes observed between A and B for wavelengths 4358 Åλ1 and 5893 Åλ2 respectively. If t be the thickness of the film, then for normal incidence2μt=n1λ1=n2λ2  or  n2=n1λ1/λ2 n2=10×4358×10−105893×10−10=7.4≈7