**·**2008-09-27 23:55:24

Fringe width is the distance between two consecutive bright or dark fringes in the Young's Double Slit Experiment.

It is caused because of successive constructive and destructive interference of light. The constructive interference of light causes bright fringe.

The method of calculation uses approximation of length. The exact method is also possible, but that is not needed unless the D is of similar order as d.!