1. The problem statement, all variables and given/known data Monochromatic light of 585 nm is shone on a slit of width 8.0 x 10^-2 mm and the interference pattern is produced on a screen 1.8 m from the source. What is the width of the first-order bright fringe? 2. Relevant equations PD/w=x/L 3. The attempt at a solution PD=? Im not sure what n would be.. thats my main problem wavelength= 5.85 x 10^-7 m L= 1.8 m w= 8 x 10^-5 m When I used n=1 wavelength, i got the right answer, but n=1 is the first order dark fringe.. can someone please explain to me this.. i would just like to know what n would be.. thankyou any help is muchly appreciated. thankyou xie xie ni mm goi!