1. The problem statement, all variables and given/known data: In a loud single mirror exp. a bright fringe of width 0.2 mm is seen at a point on the screen kept at a distance 1.0 m from the source. When the mirror is raised up to increase the angle of incidence at any point of the mirror by a dist. of 0.9 mm, fringe width of the same fringe becomes 0.5 mm, find the wavelength of the source. 2. Relevant equations: wavelenght = distance between the two slits (a) * fringe width (X) / distance from source to screen (D) 3. The attempt at a solution: How to find the distance between the two slits? Should I be proceeding by finding "a" by a= incidence angle*D?