Waves from two point sources interfere constructively and destructively as they pass each other. Constructive interference results in a bigger wave (larger amplitude); destructive interference results in a smaller wave (smaller amplitude). In some places there is no motion of the water in the ripple tank. These places are called nodes in the wave.

Two point sources give a pattern of nodal (zero amplitude) and antinodal (maximum amplitude) regions. Moving across the ripple tank from left to right, areas of minimal wave amplitude alternate with areas of maximal wave amplitude.