1) when light from a laser passes through two slits, we get two single-slit patterns that overlap2) in a double slit pattern, dark spots are where we have destructive interference, where crests meet troughs. The bright spots are were we have constructive interference, where crests meet crests or troughs meet troughs3) the positions of the bright fringes of double-slit interference is given by ym=mλLdym=mλLd, where d is the spacing between the slits4) if we increase the spacing (d) between the two slits, the spacing between the dark fringes increases; the fringes get farther and farther apart