This java applet let you play with two point sources and watch the effect of interference.
Move you mouse within the above area
The path length between mouse cursor and the two wave source are shown in unit of wavelength ( 2.2 means 2.2 times wavelength)
and click the mouse button at any point you like to start the animation. Click the mouse button toggle the animation (resume/pause). You can click at the right point source, and drag the mouse button to change its location. Enter the value in the textField to change the wavelength. Click Reset for default values. Click show path-lengthto display the path-length difference during animation.