## Refractive index

How can one measure refractive index by knowing the change in angular range of the first dark bands of an interference pattern(single slit diffraction), when the apparatus is change from air to under water?

I think I missed that lecture, and I am still catching up.
 PhysOrg.com science news on PhysOrg.com >> King Richard III found in 'untidy lozenge-shaped grave'>> Google Drive sports new view and scan enhancements>> Researcher admits mistakes in stem cell study
 Recognitions: Gold Member Homework Help Science Advisor Staff Emeritus You need to know that it's the wavelength, not the frequency, that changes when the refractive index changes. If light has wavelength $\lambda$ in vacuum, then it has wavelength $\lambda^{\prime}=\lambda/n$ in a medium of refractive index $n$.