Physics of Sound: Demonstrations

Standing waves

Superposition of two plane waves propagating in different directions (red and blue) results in a standing wave (black). Standing wave has nodes and antinodes indicated by dashed lines. In the nodes the amplutude of the standing wave is zero while in the antinodes it is maximal.

Usually standing waves satisfy boundary conditions at the borders of the region where they exist. For instance, a string fixed at its ends has a zero vertical or horizintal deviation at the fixation points. In this case the standing wave has nodes at the ends, as shown below.