Interference

This app shows interference. Interference happens whenever two or more waves meet at the same point at the same time. In this app two waves with identical frequency and wavelength sum to form the dark green wave shown at the bottom of the screen. The incident waves have the same amplitude and the same average value, but they are shown with a little shift to make them more visible.
Change the relative phase acting on the slider and see what happens to the sum of the red and blue waves.