Module 8—Mechanical Waves
Lesson Summary
As you worked through this lesson, you should have developed answers to these questions:
- How is a standing wave produced in a closed-air column?
- What is the relationship between wavelength and air column length for a closed resonating air column?
- How is a standing wave produced in an open-air column?
- What is the relationship between wavelength and air column length for an open resonating air column?
A sound wave will travel through a closed-air column until it reaches the closed end, where it is reflected. The reflected wave will encounter other incoming waves, and interference will occur to produce a standing wave pattern. The closed end of the air column serves as a fixed point (node), with alternating points of complete destructive interference (nodes) and points of complete constructive interference (antinodes) extending towards the open end of the air column.
A closed-air column will only resonate when an antinode is located at the open end. This is observed as an increase in volume when both the air column and the sound source (tuning fork) are producing identical sound waves. This occurs when the air column length (L) is 
times the length of the standing wave (λ).
An open-air column will hold a standing wave in a similar way to that of a closed-air column. Alternating points of complete destructive interference (nodes) with points of complete constructive interference (antinodes) extend throughout the air column.
An open-air column will only resonate when an antinode is located at both open ends. This is observed as an increase in volume when both the air column and the sound source (tuning fork) are producing identical sound waves. This occurs when the air column length (L) is 
times the length of the standing wave (λ).