- William C. Evans
This applet shows several constructive interference bands, on a horizontal scale in millimeters, for adjustable light wavelength ("lamda", in 1E-7 meters), double-slit separation distance ("dist", in millimeters), and slits-to-screen distance ("R", in meters). The destructive interference, or cancellation, bands would appear halfway between the bright bands shown here. For background on the calculations, see, e.g., Section 37-3 of Sears and Zemansky, 10th Edition. For the fall-off of intensity, see Eq. 38-12 in that book (in the applet this is just simulated by arbitrarily reducing the thickness of the segments).