This lab shows interference of waves from two identical sources that are separated by a variable distance. The wave crests are shown in red and the troughs in blue, with black indicating a local wave amplitude of zero. (Note that the entire image updates instantly when you move the slider because it is drawn using a formula that assumes fixed separation, rather than from a simulation of the time-dependent response of the wave medium. Note also that the wave amplitude does not decrease with the distance from the source, as it would for physical waves.)