1. The problem statement, all variables and given/known data Light of wavelength 680 nm falls on two slits and produces an interference pattern in which the fourth order fringe is 38 mm from the central fringe on a screen 2.0 m away. What is the separation of the two slits? 2. Relevant equations d * sin(theta) = m * lambda 3. The attempt at a solution I tried to calculate the slit separation using the equation above but I'm not sure about the angle. Using tan^-1(.038/2), I got an angle of 1.1 degrees which then led me to a d value of 1.41 x 10^-4 m, but the answer given by the book is .085 mm so I'm just completely lost at this point.