AP EAPCET 05-Jul-2022 Shift 1 Paper

Young's double slit experiment is conducted with monochromatic light of wavelength 5000Å, with slit separation of 3mm and observer at 20cm away from the slits. If a 1mm transparent plate is placed in front of one of the slits, the fringes shift by 6mm. The refractive index of the transparent plate is