Light of wavelength 476.1 nm falls on two slits spaced 0.29 mm apart. What is the required distance from the slits to the screen if the spacing between the first and second dark fringes is to be 4.2 mm?

The distance is

Explanation:

From the question we are told that

    The wavelength of the light is  

      The  distance between the slit is  

       The  between the first and second dark fringes is  

Generally  fringe width is mathematically represented as

Where D is the distance of the slit to the screen

   Hence

substituting values