Question

A 50cm long hollow glass cylinder is open at both ends and is suspended in air. A source o sound that produces a pure frequency is placed close to one end of the tube. The frequency of the sound is slowly increased from a very low value. The tube is first observed to resonate when the source frequency is 320Hz.
(I) The speed of the sound in the tube must be:
A: 320m/s

(II) The frequency of the source is slowly increased until resonance occurs again FOR THE THIRD TIME. The frequency at which this happens is:

(III) THe frequency when resonance occurs for the FIFTH time is:

Answer 1

open at both ends? the tube must be lambda/2 long

frequency*wavelength=velocitysound
320*2*.50=...

at the the the key to the second part is to realize the fundamental, the path is one wavelength (length of tube is half that). THe second harmonic, path must be two wavelength (tube is one wavelength), the third harmonic is when the path is three wavelengths (length)is 1.5 wavelength), fourth harmonic is when path is four wavlengths (length is 2.0 lambda), and so on