Which equation should be use to find L, the length of pipe he needs to have to produce sound

Question

James wants to produce a sound t hat has a wavelength of 20 cm.  The pipes he has all have width of 3 cm

Answer 1

The length of the pipe has to be 4 times the wavelength. This is because the sound wave consists of nodes (fixed points) and antinodes. Nodes occur at the closed end of a pipe and antinodes at the open end and the distance between node and antinodes is quarter of a wavelength. The pipe needs to be 80cm long or some multiple thereof to facilitate a wavelength of 20 cm. The width of the pipe governs the amplitude of the sound. The equation is L=4n(lambda) where lambda is the wavelength of the sound.