Two Source Interference

BACK OF TANK (screen position)

Both sources

Left source (1)

Right source (2)



The animation above simulates the wave patterns produced by two sources of water waves in a tank. You are looking down onto the water from above. The two sources in the above animation produce wave crests simulaneously.

The two point sources act very much like light passing through a double slit. The light interference pattern of bright and dark fringes seen on the screen would be similar to looking at the wave pattern along the back of the water tank (the top of the simulation). Wave crests appear white and wave troughs appear black, while positions of complete destructive interference appear grey.


First examine the interference pattern with both sources turned on.  Use the "Edit" button to reposition the sources by draging the red dots.

Use the simulation to help you determine what changes would be seen in a light interference pattern (similar to today's experiment), when the slits (the point sources) are:

  1. closer together?
  2. farther apart?

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