Hey, I have a problem here involving single slit diffraction, and it's stumped me. A single slit is illuminated with a 660-nm light, and the resulting diffraction pattern is viewed on a screen 2.3 m away. If the linear distance between the first and second dark fringes is 12 cm, what is the width of the slit? I want to use this formula to start me off: y= L tan (theta) But what value of y should I use? It can't be 12 cm, because that's defining the distance between those two dark fringes, not their distance to the central bright fringe. Any ideas?