What happens when waves collide? Try out this activity to see how waves in a ripple tank behave when they cross paths.
When the straight-line waves diffract through the two openings, two sources of semicircular waves are created. When the crest of a wave from one opening meets the trough of a wave from the other opening, they cancel each other out, producing a dark spot on the screen. When a crest of a wave from one opening meets the crest of a wave from the other opening, they add together to make a bigger crest, producing a bright spot. When there are lots of waves from two sources, there are lots of crest-trough and crest-crest meetings, producing dark and light patterns called interference bands or fringes.
We demonstrated diffraction in our ripple tank because it is an easy way to produce two sources of identical waves, and identical waves work best for showing the way waves interfere with one another. Interference patterns between waves can happen no matter how the waves are generated.