This document discusses the principle of superposition of waves and the formation of stationary waves. It defines superposition of waves as the vector sum of individual displacements from different waves. There are two types of interference - constructive and destructive - depending on whether the waves are in phase or out of phase. A stationary wave is formed when two progressive waves of the same amplitude and wavelength travel in opposite directions. The stationary wave has nodes where the amplitude is minimum and antinodes where it is maximum.