1. The problem statement, all variables and given/known data A double-slit interference pattern is observed on a screen 1.0m behind two slits placed on 0.3mm apart. Ten bright fringes span a distance of 1.65cm. What is the wavelength of the light? 2. Relevant equations Since we're looking at bright fringes: (m+1/2)[tex]\lambda[/tex] = dsin[tex]\theta[/tex] = d(x/L) 3. The attempt at a solution d = 3E-4m m = 4 (I feel like I'm supposed to use just one half of the bands, excluding the middle band. Is this right? Why do I do this?) L = 1.0m y = 8.25E-3m (this is the spread of the 10 fringes divided by 2 since I'm using half of them) (m+1/2)[tex]\lambda[/tex] = d(x/L) (4+1/2)[tex]\lambda[/tex] = 3E-4(8.25E-3/1.0) [tex]\lambda[/tex] = 5.5E-7m On my formula sheet there is an 'x'...the variable for the spread of the fringes is traditionally 'y'...I figured they were just the same thing so used y for x in the above example. If that's wrong then could someone explain where I get 'x' from? Any explanation would be appreciated. Thanks!