Wave Optics

Step 1: Experimental Setup.
Consider two coherent sources and separated by a distance . Let be the distance between the slits and the screen. A point is located on the screen at a distance from the central maximum .

Step 2: Finding the Path Difference.
The path difference between the waves reaching from and is . For , this path difference is approximately: $ \lambda y_n n^{th} \beta n^{th} (n+1)^{th} $ This expression shows that the fringe width is constant for a given experimental setup.