Standing waves in air column is an example of longitudinal standing waves. When any source of sound is brought near the air column then there is generation of compression and rarefaction in the column. These waves are reflected from the other end of air column. By the superposition of incident waves and reflected waves longitudinal standing waves are produced. Air columns are of two types:
- If one end of the pipe is closed and the other is open, then it is called closed organ pipe and its air column is called closed air column.
- If both the ends of the pipe are open, it is called open organ pipe or open air column.
To know about the modes of vibration in an air column, following facts have to be known:
- At the closed end of the pipe the air particles cannot vibrate hence this end should have node.
- The open end of the pipe is in contact of the atmosphere hence the change in density at this end should be zero or we can say that the strain here should be zero and there should be antinode at the open end.
- There should be an antinode between two nodes and a node between two antinodes.
