Young's double slit experiment is conducted with monochromatic light of wavelength 5000$$\mathop A\limits^o $$, with slit separation of 3 mm and observer at 20 cm away from the slits. If a 1 mm transparent plate is placed infront of one of the slits, the fringes shift by 6 mm . The refractive index of the transparent plate is

In Young's double slit experiment the slits are 3 mm apart and are illuminated by light of two wavelengths $$3750 \mathop A\limits^o$$ and $$7500 \mathop A\limits^o$$. The screen is placed at 4 m from the slits. The minimum distance from the common central bright fringe on the screen at which the bright fringe of one interference pattern due to one wavelength coincide with the bright fringe of the other is

When monochromatic light of wavelength 600 nm is used in Young's double slit experiment, the fifth order bright fringe is formed at 6 mm from the central bright fringe on the screen. If the experiment is conducted with light of wavelength 400 nm from the central bright fringe, the third order bright fringe will be located at