Kundt's tube can be used to demonstrate sound wave superposition and standing waves. The signal generator is turned on to about 100Hz (which is a frequency easily audible to humans). Then the adjustable end is moved until a loud sound is heard. This loud sound is a result of making the length of the tube system a multiple of sound wavelengths. When this natural frequency is heard, the dust or talc will form equally spaced piles (nodes) and in between these nodes will be areas of little or no dust (antinodes). The distance between nodes can be measured to be the sound's wavelength/2.