In our physics lab, we were given several different kinds of thin slits which we were to place in the path of a 632.8 nm laser to observe the effects of diffraction and interference. We had four metal cards with the following properties: Card A: 2 slits (0.25 mm spacing, 0.04 mm slit width) Card B: 2 slits (0.50 mm, 0.04 mm) Card C: 2 slits (0.25 mm, 0.08 mm) Card D: 2 slits (0.50 mm, 0.08 mm) We found that Cards A and B had central and secondary maxima that were equal to one another in length, and the same for Cards C and D. In other words: Card A: Central = 2.0 cm, Secondary = 1.0 cm Card B: Central = 2.0 cm, Secondary = 1.0 cm Card C: Central = 1.0 cm, Secondary = 0.4 cm Card D: Central = 1.0 cm, Secondary = 0.4 cm However, the equation used to determine the fringe width is: x = (Dh)/d Where D is the distance from the screen to the slits (61.7 cm), h is the wavelength, and d is the slit spacing. Doesn't this imply that the maxima widths are determined by the slit spacing, which would mean A and C should be the same and B and D should be the same? Am I getting the term "fringe spacing" confused with maxima length or something? Others in my lab have the same results and do not know what to do either.